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Limiter trouble shooting

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.

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


A-body rallye dash limiter fix




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:

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:

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:

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).

Advantages of our limiter over mechanical limiters:

Advantages of our limiter over linear home made limiters: