RTE Gauge Faq
From RTE
Limiter trouble shooting
- ) If the new solid state limiter doesn't function (LED doesn't blink), remove the limiter to gage wire from one gage at a time checking to see if the limiter
begins operation. The limiter will detect a short circuit and turn itself off until the short is removed. Also, if the limiter has too much or not enough voltage, then it will turn itself off.
- ) Note that some mustangs had build in resistance wire feeding the limiter. This wire must be removed or shorted around in order to make our solid state limiter work properly. The reason is that our limiter will see the voltage drop in the resistance wire, and it will think that the voltage is below 9V, so it will turn itself off to protect the limiter and the gauges.
Information on Mopar Ammeters, and Voltmeter conversions
- ) All vintage mopars should have their ammeter back replacted with a bonded stud back. Currently most factory ammeters have about 10 to 20 Milli-Ohms resistance. Bonding the studs to the ammeter frame reduces the resistance down to 1 -2 milli ohms. Real Time Engineering can rebuild your ammeter with a bonded stud back for $60.
- ) If you plane on using over about a 70 amp alternator, then you should switch the ammeter over to a voltmeter.
The original ammeter in all the Vintage mopar product has a bad reputation because many times people have seen these ammeters fail. Here is our thoughts on the ammeter:
The original design of the ammeter actually has a flaw in it, in my opinion. A much better design would have been to bond the studs to the copper in some way instead of relying on the cardboard back piece to hold the studs to the copper frame.
- Is the current rating of the ammeter being exceeded? The original ammeter spec for most mopar ammeters is +-40 amps. In other words, 40 amps will make the ammeter read full scale. The ammeter can probably tolerate as much as 60-70 amps with no harm (if it is a bonded stud ammeter), but it is not a good idea to run 100 amps through the ammeter. Some ammeters I have seen will have a small copper strip across the back of the ammeter, which will make the ammeter able to handle more than 40 amps before reading full scale. However, these ammeters with the strip still use the cardboard to hold the studs onto the ammeter copper body, so that the limiting factor is going to be the resistance between the studs and the copper ammeter body. If the studs had been bonded to the copper, then there would be very little resistance and the ammeter design would have been able to handle more current without getting hot.
- Are the wires going to the ammeter tightly coupled? If the wires going to the back of the ammeter are not tightly coupled by properly tightening the nuts, then there will be extra resistance. Extra resistance equates to heat being generated when current goes through the wires, which can lead to fire. Bottom line, make sure the nuts are tight on the ammeter.
- What should I do if I want to run a 100A alternator? In my opinion, you should modify the wiring in the car so that some of the current from the alternator goes from the alternator directly to the battery. This will do two good things for you: 1) It will make sure you don't have 100A going through the two firewall connectors, which were never designed to handle 100A. 2) It will make sure that the ammeter is not seeing 100A, which it was never designed for. The best thing to do is to run a wire from the back of the alternator over to the stud on the starter relay. This will shunt most of the current straight into the battery, and it will keep the protection of the fusible link that is between the battery and the starter relay. To the best of our current knowledge, there is no reason to put a relay into this new wire, as some people are recommending.
- Should I switch over to using a voltmeter? I personally think that an ammeter gives you more information on the state of the battery and the charging system than a voltmeter does. RTE is now offering voltmeter conversion kits for most mopar cars for $150.
- Here is a nice chart showing how the resistance of the ammeter versus the power and voltage drop works. As stated previously, we highly recommend that you have your ammeter rebuilt by us so that you stay in the green region of this chart:
Easier to read PDF of this same chart: media:AmmeterWattages.pdf
Can you change the graphics on a Ebody rallye and non-rallye speedometer to metric (KPH)?
Yes, I can silk screen the speedometers in KPH. We charge an extra $30 to do this over our normal charges. The speedometer will be properly calibrated in KPH. However, the odometer will not be calibrated properly because it takes a custom worm gear inside the speedometer to calibrate the odomoter to kilometers and this part is no longer available. In other words, the odometer and trip meter will continue to read out in miles.
How to convert Ebody non-Rallye dash harness to Rallye dash harness
- change oil pressure senders
- cut the wires off the oil light
- connect the grey oil light signal wire to the oil gauge connect the dark blue oil light wire to the tach power. (this wire is 12V ignition switched)
- run the tach signal from the negative coil post to the tach
- splice 12V continuous power from the cigarette lighter to the clock
Here is a diagram showing how to do this is more detail:
Also, we now sell a kit with the correct wires to make this work here:
More info on speedo and tach needles
- Reason 1 why speedo needles break: If the speedometer cable is dry and needs to be lubed, sometimes the cable will bind and then jump forward, causing the speedo needle to swing wildly and break.
- Reason 2 why speedo needles break: If the nylon bushing inside the speedometer is worn out and it allows the aluminum cup to touch the rotating magnet then the speedo needle can break. Another possible cause of trouble here is if the metal shaft in the speedometer gets rusty, then it takes a lot more force to move it, which can cause the the speedometer cable to twist up, then unspool quickly.
- Reason 3 why speedo needles break: If there are metal shavings or rust pieces stuck to the magnet which allow friction with the aluminum cup, then the speedo needle can be broken.
- Reason 4 why speedo needles break: If there is a problem with the gear inside the transmission it can cause the needle to break. Thanks to the tachman for this bit of info: http://www.tachman.com
How to remove Tach and Speedo needles from Mopar speedometers
- Take the speedo out of the instrument cluster
- Grab the aluminum wheel in the back of the speedo with one hand and don't let it move.
- Grab the speedo needle with your other hand, holding only the black round part, and twist the needle back and forth and gently pulling the needle off the stem.
- Put it back on the same way except push on it.
The only danger here is that you might bend the needle pointer/tail, so it is best not to touch that part of the needle.
You can remove the tach needles the same way, but you don't need to hold the back of the tach. Instead just twist the tach needle past 0 RPM while gently pulling on the needle.
General guidelines to gauge testing on vintage mopars
- Run the speedo by taking an old speedo cable and cutting it off and mounting it in a drill. See if the speedo will run at 1 good speed without jumping around when the drill is full speed. Sometimes speedometers will allow the magnet to contact the aluminum wheel, which then breaks off the speedometer needle. RTE sells a replacement needle made out of stainless that won't break. Many times if this happens you need to use an air compressor to remove any ferrous particles that are attached to the magnet, and lubricate the speedometer. RTE has some spare Speedometer parts, contact us if you need a part.
- Run the tach from another car, connecting up the long stud to +12, the case of the tach to ground, and the short stud with the spade terminal to the minus side of the coil. Use a dwell tach to see if the tach is accurate. (We sell a kit to fix this up if it is not working or in-accurate). If you have a RTE tachomter kit in your tach, then you can use our tach calibrator to test the tach as well.
- On the Fuel/oil/temp gauges, put 9V or 12V across them for 1 second, and if the hands move then they are good. (This does not test the calibration, but that is more complicated). DO NOT leave the 12V on the gauges for more than 1 second. Also, the Fuel/Oil/Temp gauges can be calibrated full scale by using a 10 Ohm resistor to ground and hooking up the limiter to the gauge. The gauge should read full scale in this case. Note that we recommend that you use a battery, do NOT use a battery charger when testing gauges. Battery chargers do not have a good clean 12V coming out of them.
- Test the limiter by putting 12V into it, grounding the limiter case, and seeing if the output goes off and on and off every 1-2 seconds, using a test light. If it is stuck on 12V, then the limiter is bad and it will fry your fuel/oil/temp gauges. Again, do not use a battery charger to supply the 12V.
- Take the ammeter out of the housing, and look and see if it has any corrosion on it (do NOT use a corroded one in a car, it can catch on fire). Also gently wiggle the two studs, and if either stud moves, DO NOT use this ammeter in your car as it can catch on fire. I can rebuild these if you have a bad one. Also, make sure that the needle points to zero as you tilt the ammeter around. If the needle moves and points far to the left and right, then the magnet in the ammeter is bad and you need a new ammeter.
- If you have a clock, put +12V to it, and ground the case, and see if the clock runs. If it does not, we have a kit with detailed instructions and pictures where you can fix it.
I always take my switch backs off and bead blast the switches, then clean them, then put a lot of dialectric grease back in them and put them back together. You can also test the switches with a continuity meter after you have them back together, take some notes about what should be connected when you have the switch apart.
Fixing dash clusters that have internal limiters
PDF copy of this same info: media:InternalLimiter.pdf
Some of the cars made my Mopar did not use external limiters. Instead these cars built the limiter into one of the gauges, usually the fuel gauge. Cars in this category include the 66/67 charger, 68-74 ABody cars with Rallye dash, and some older imperials.
When these internal limiters go bad, you have two choices, either replace the whole gauge (expensive and hard to find!), or disable the limiter built into the gauge and wire in an external limiter. If you decide to wire in an external limiter, then you should verify that the gauge still functions as a gauge, i.e. that it hasn't been burned out when the limiter failed. Another thing to consider is that it might be good insurance to just disable the internal limiter and replace it with an external limiter before the internal limiter fails. Here are some pictures showing how RTE disabled the internal limiter in an older Imperial dash cluster, and wired in an external solid state limiter. Real Time Engineering can do this for you for $50 labor plus the cost of the solid state limiter. The red arrow shows how we bent the internal limiter bi-metallic strip to disable the internal limiter.
Imperial internal limiter fix
![right]](/mediawiki/index.php/Image:Imperial2.jpg)
A-body rallye dash limiter fix
- Step 1: Take the fuel gauge out of the cluster, and gently take the face off.
- Step 2: Bend the limiter points out of the way, so that they no longer contact. Make sure that the points don't touch anything.
![200px]](/mediawiki/index.php/Image:AbodyRallyeLimiter2.jpg)
- Step 3: Put the Fuel gauge face back on.
- Step 4: Mount the IVR3 (Ebody) style limiter using one of the circuit board ground mounting points.
![200px]](/mediawiki/index.php/Image:AbodyRallyeLimiter3.jpg)
- Step 5: Run a wire from the 12V stud going into the fuel gauge to the IGN terminal on the new solid state limiter. Use a ring terminal on the fuel gauge side, and a male spade terminal on the limiter side.
- Step 6: Run a wire from the old fuel gauge limiter output stud to the solid state limiter output terminal. Use a ring terminal on the fuel gauge side, and a female spade terminal on the limiter side.
![200px]](/mediawiki/index.php/Image:AbodyRallyeLimiter4.jpg)
- Step 7: Test the setup by turning the key on in the car. The fuel gauge, oil gauge, and temperature gauge should operate properly, and the red LED on the new solid state limiter should blink after the 3-6 second warm up time.
More information about dash limiters
On the back of most mopar dashes (with some notable exceptions) there is a 1" X 2" metal can, with 3 terminals. This device is known as a limiter. Its function is to regulate the voltage that is being applied to the fuel/oil/temperature gauges.
Some mopar dashes don't have a visible limiter device. Instead they have the limiter built into the fuel gauge. These special dashes can be identified by looking at the fuel gauge, and if it has 3 terminals then it has the limiter built in. A-Body Rallye dashes and 66/67 Chargers are two examples of dashes that have the limiter built into the fuel gauge.
The 70-71 parts book does list 4 different types of limiters, of which we have seen only two types. The E-body limiter has part number 2209216, and the most common push in type has part number 2258413.
The push in type is intended to be pressed into some mounting clips on the backs of the circuit boards. This type of limiter has three male spade terminals protruding from the face of the limiter. One terminal is spot welded to the case for ground. The other two terminals are for +12V in, and limited voltage out. There is usually a capacitor connected to the +12V spade when it is pressed in palce. This type of limiter is always found on dashes that have circuit boards. This type of limiter was used on a lot more different types of mopars than the other type, and this type of limiter is still available at your auto parts store.
The E-body limiter has a mounting tab spot welded to the back of the limiter. A small 1/4" head bolt is used to fasten this type of limiter to the metal dash frame, and this is how this type gets it ground. The +12V input terminal on this limiter is a dual male spade terminal. It has two terminals so that one can be +12V input, and the other is intended to be connected to the capacitor (sometimes called a condensor). The capacitor does not have any effect on the operation of the limiter, but is intended to stop AM radio interference. The 2nd terminal on this type of limiter is a female spade terminal, and this is the limiter output to the gauges. This type of limiter was used on just a few different types of cars, includingthe 70-74 E-bodies. This type of limiter is no longer available in the aftermarket. Note that there is a limiter that appears to be the same that was used for some ford dashes, but this limiter does not put out the correct voltage and will make your gauges read low if you try to use it.
In order to understand the limiter and why it is necessary to have one on your dash, it is first necessary to understand how the fuel/oil/temp gauges work. The typical Fuel/Oil/Temp gauge (henceforth referrred to as FOT) has inside it a bi-metallic strip, similar to the bi-metallic strip inside your non-electronic wall thermostat. There is some insualed nichrome wire wrapped around the bi-metallic strip. When current is run through the nichrome wire, it will heat up the bi-metallic strip, causing it to bend. The bending is caused because one of the types of metal expands faster than the other. See this URL for more info on how bi-metallic strips work:
http://en.wikipedia.org/wiki/Bi-metallic_strip
One important thing to know about bi-metallic strips is that the amount they bend is proportional to the amount of heat that is put into the strip. Therefore, if you want to have an accurate gauge, you must have accurately regulated heat. The heat is proportional to the current through the wire, and the current through the wire is dependant on the voltage being applied to the wire. Therefore if the voltage being supplied to the gauges were to vary, then the gauges reading would vary. It turns out that the voltage on a cars battery is not very well regulated, and it can change as much as 2-3 volts under different conditions (for example, just turning on the headlights and sitting at idle will have a lower voltage condition). Therefore the limiters job is to regulate the voltage being applied to the gauges, so they will be accurate and not vary.
The dash limiter is not temperature sensitive. In other words, if the external temperature varies between its normal extremes of +150F and 0F, the limiter will still put out its voltage with little or no variation. This temperature compensation is accomplished by the way the bi-metallic strip is constructed inside the limiter. The FOT gauges also have this temperature compensation inside them and so are not sensitive to the external temperature.
The way the dash limiter works is as follows. When power is first turned on (i.e. you turn on the key), then the points are closed because the bi-metallic strip is not yet hot and the limiter is putting out +12V. The nichrome wire inside the limiter starts to heat up, which in turn starts to heat up the bi-metallics strip. After about 3-4 seconds, the strip will get hot enough to cause it to bend up and open the set of points inside the limiter. When the points open. When the points open, then the nichrome wire stops heating the strip, and the limiter stops putting out +12V. The amount of time that the limiter stays open is proportional to the amount of heat that was put into the strip, so when the voltage of your car battery is higher, then the limiter stays open longer, thus regulating the average RMS (Root-Mean-Square) voltage coming out of the limiter.
There are several different failure modes that a limiter can have:
- If the limiter loses its ground (from corrosion for example) then there will be no current flowing in the nichrome wire, and the limiter will output +12V all tht time. The FOT gauges cannot tolerate this condition for more than about 20 seconds, and will burn out after about 20 seconds.
- If the nichrome wire burns in half or breaks due to mechanical vibrations, then the points will no longer open and the gauges will fry after 20 seconds.
- If the points weld themselves shut, then the points will no longer open and the gauges will fry after 20 seconds.
- If the output of the limiter is shorted to ground, then either the fuse to the instrument panel will open, or we have seen some limiters that had the bi-metallic strip burned in half. In this case the gauges won't be fried, but they will stop working until the limiter is replaced.
Currently there are some people that are replacing the insides of the limiter bi-metallic strip with a linear regulator. This does work, but it is not a perfect solution. The following problems exist with this solution:
- The linear regulator will dissipate a lot of heat because it is constantly dropping a lot of voltage across it in order to create 5V all the time. In fact a linear regulator will generate a lot more heat then the original limiter. It is necessary to thermally bond the linear regulator to the limiter case to keep the regulator from getting too hot under normal operation. For reference, it takes about 300mA per gauge to make each gauge read full scale. Therefore the amount of heat generated by the linear regulator is P=IV=300mA*(12V-5V)*3=6.3Watts. This is a lot of heat.
- The linear regulator requires a good ground just like the original limiter. If the ground is lost, then the linear regulator will put out +12V all the time, frying the gauges.
- The linear regulator will not properly emulate the original limiter in the sense that the original limiter puts out +12V for 3-4 seconds at initial power up in order to get the gauges up to their correct reading quickly. It can take up to 1 minute for the gauges to reach their final reading when using a linear regulator after turning on the key.
- The original mechanical limiter pulses on and off, and this has the effect of overcoming friction inside the FOT gauges. This makes the gauges more responsive to changes. Since the linear regulator doesn't pulse, it doesn't have this effect.
- Rarely some linear regulators can fail when their output is shorted to ground. Usually when they fail, they will short the input to the output, causing +12V on the output of the regulator.
- On a positive note, most linear regulators have heat sensors inside them and will shutdown when they get too hot (caused by the output being shorted to ground).
Real Time Engineering has a new solid state limiter that will replace the original mechanical limiter on the back of your dash. This new limiter has many advantages over the original limiter, and also has advantages over the linear regulators that hobbyist have been using as well. The biggest advantage is that our limiter doesn't have a mechanical set of points and a heater wire that can break and fry your gauges (which is what the original mechanical limiter had).
- Our limiter exactly duplicates the original limiters function by slowly switching 12V on and off.
- Our limiter has a built in polyfuse which protects the limiter and your wiring from short circuits on the output of the limtier
- Our limiter constantly looks for short circuits on the output of the limiter and will switch itself off if a short circuit is detected. When the short is removed, then the limiter starts working again.
- Our limiter has a built in diagnostic LED that blinks when the limiter is on, helping you see that you have power to your dash and that the limiter is operating properly.
- Our limiter has a warm up time at turn on, same as the original mechanical limiter. This means that your gauges will come up to the proper reading very quickly.
- Our limiter is always outputting a constant 5V average, no matter what the input voltage is (Within the range of 9V to 18V). If the input voltage goes too high or too low, then the limiter shuts off.
- Our limiter output is constant regardless of temperature.
- Our limiter is not sensitive to mechanical vibration.
- If our limiter loses ground, it will shut itself off. Contrast this to the mechanical and linear limiters, which will put out 12V and fry your gauges.
- If the alternator and/or the firewall regulator go bad and the alternator puts out too much voltage (over 19V), then our limiter will cause the instrument panel fuse to open, protecting the limiter and the gauges. Note: It is important that you have the proper size fuse in the fuse box for the instrument panel for this reason.
Advantages of our limiter over mechanical limiters:
- Won't fry your gauges when ground is lost
- No mechanical moving parts to wear out
- No points to stick closed
- No nichrome wire to break and then fry your gauges
- Insensitive to heat and cold
- Solid state so should last a very long time
- Short circuit protected
- Diagnostic LED built in
- Uses less current than the original limiter (because there is no heater wire)
- Original mechanical limiters tend to vibrate badly and lose regulation temporarily when going over very rough roads.
Advantages of our limiter over linear home made limiters:
- Won't fry your gauges when ground is lost
- Doesn't generate any heat (linear regulators make a lot of heat)
- Has a warm up period when turned on to make the gauges come up fast
- Diagnostic LED built in
- Uses a lot less power (Linear regulators can waste up to 8W of power in this application)
Information about AMX/AMC CVR limiters
RTE also offers a CVR limiter rebuild service for $50. If you send us your old CVR limiter, we can put our new solid state limiter board into the CVR metal can. Contact us for this service.
Here are two images of what the CVR limiter looks like:
Information about Volvo Limiters
We can use our solid state voltage limiter inside of the volvo can, as long as you send the can to us. We can do this conversion for $50.
Information about how the Mopar RT/SE and Grand Coupe Low fuel light relay #2983828 works
Here is a picture of the low fuel light relay insides:
Theory of operation:
- +12V Power us fed into the IGN and COM terminal when the key is turned on.
- Vehicle Ground is connected to the GND terminal through the case of the relay.
- The GAGE terminal is connected to the fuel gauge, where the limiter would be connected in a normal car that did not have a low fuel feature.
- The other side of the fuel gauge is connected to the standard Mopar fuel sending unit, same as in any mopar. The fuel sending unit will have a resistance of approximately 10 Ohms when full and approximately 80 ohms when empty.
- The LAMP terminal is connected to the low fuel light lamp.
- There is a coil of magnet wire between the IGN terminal and the interior point labeled X that is about 6 Ohms. The resistance of the X coil, the middle heater, the resistance in the fuel gauge, and the sending unit resistance all add up to control the amount of current going through the middle heater coil when the limiter is in its on state.
- The X terminal feeds voltage into the middle heater coil when the top bi-metallic strip (limiter) is closed, when tends to open the bottom points. When the bottom points are open, then the low fuel light is off. The fuel sending unit being at full (10 Ohms) means that a lot of current goes through the middle heater strip, keeping the bottom bi-metallic strip strongly open. Note that the middle heater strip is only on when the voltage limiter is on.
- The top bi-metallic strip is in fact a voltage limiter, just like the limiter on the back of your dash. The only difference between the standard voltage limiter and the limiter inside this relay is that this limiter is set to stay on longer to compensate for the voltage loss in the X coil and the middle heater strip. In other words, it is set to deliver the same amount of power to the fuel gauge as a standard limiter would, even though there is the added resistance of the X coil and the middle heater strip.
- The bottom bi-metallic strip is a latching relay. It is open when there is enough average current in the middle heater coil to make it stay open. The current in the middle heater coil is controlled by the fuel sending unit resistance. When the fuel sending unit resistance gets high enough so that the middle heater coil allows the bottom strip to close, then the bottom bi-matallic strip feeds power to the LAMP terminal through the bottom heater. When the LAMP is lit, this causes the bottom heater strip to heat up which tends to force the bottom bi-metallic strip to stay closed, acting as a hysteresis element. This is needed to make sure the low fuel relay won't open and close as the limiter turns on and off.
- There is a small amount of voltage loss in the bottom heater strip, which will cause the low fuel light to be slightly dimmer than all the other bulbs in the car. This bulb is a standard 14.4 Volt bulb, number 1892-USA part number. The resistance of this bulb is important in that it helps set the current in the bottom heater coil. The resistance of the lamp is listed as 120 Ohms (cold?). The resistance of the bottom heater when cold is about 1 Ohm.
- RTE will eventually make a replacement circuit board for this relay for all those people out there who need a new relay, or who would just like to add a low fuel light to you car. When we make this board, we will make it so that it can go into the original low fuel relay metal can, and we will also have some 4-40 holes in the board so that those of you without the relay metal can will be able to mount the board under the dash.