You may want to consider changing out the factory Instrument Voltage Limiter a.k.a. Instrument Voltage Regulator (IVR) with a solid-state regulator.
The original IVR is a bi-metallic strip style regulator and it is horrible at regulating the 5 volts DC.
Solid-state IVRs are available as part number IVR3 from RTE for E-Bodies.
Real Time Engineering
There are many other reasons to upgrade it. This
Mopar Collector's Guide article has good info, too.
RTE's website has this information on the E-Body IVR:
"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 its 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 condenser). 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 5V DC limiter output to the gauges. This type of limiter was used on just a few different types of cars, including the 70-74 E-bodies."
INSTALLATION OF IVR (same as factory IVR a.k.a. limiter):
"Connect the condenser to one of the two male spade terminals. The main under dash harness plugs into the other male spade terminal, supplying 12VDC to the limiter. The small wiring harness that powers the fuel/oil/temperature gauges should be plugged into the single female spade terminal."
Good luck and let us know how everything turns out.
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