66-67 Dodge Charger Source Guide

Most Mopars have an external style voltage limiter that plugs into the rear of the instrument clusters. Someone at Chrysler in their infinite wisdom decided that they would incorporate the limiter inside the dash fuel gauge on the first generation Chargers. If the factory limiter for some reason fails, you will get a full dose of battery voltage through the fuel, water, & oil pressure gauges thus letting the "smoke" out of them rendering them useless. How the originals fail is the "points" inside the fuel gauge for the limiter stick closed for a time and send full battery voltage through the 34 gauge silk wrapped ni-chrome special wire that is wrapped around the bi-metal strip in there. All it takes is a few seconds and "POOF" - gauges fried.

The limiter acts like the turn signal flasher does, it makes & breaks contact inside thus only allowing about 5 volts through the little fragile wires inside the gauges. What I have done is this....I get one of the "plug-in" style limiters, take it apart and remove the "points" strip....put it back together, and install a 5volt transistor along with a capacitor and mount it to the "plug-in" style limiter. The transistors I use are good all the way up to around 20volts I believe. What you would need to to to install one of these is first you have to do a little surgery on your fuel gauge and remove the limiter portion of the gauge, put the gauge back together, and mount the limiter I build to the rear of the dash and wire it into the fuel gauge pegs.

I picked up a limiter from NAPA for $25.00 bucks
Part #: IR9

It drops 12v to 5v to the fuel, oil & temp guages. We have an antique one that is of 1967 era technology... when the old one goes it sends 12v to the guages and fries them! this replaces the old one...takes some work...remove the cluster etc...

No original wires in the car will be cut or spliced. The twin plug on the fuel gauge containing the "5v" and "S" wires will remain plugged to the cluster as usual. The "+V out" wire on the regulator will be tied into the "5v" pin on the cluster. (see photo) Insulating the old "12v" pin on the cluster might be a good idea. Power could back-feed out of it should the original limiter decide to work again.

The "12v" wire in the car will connect to the regulator, not the pin on the fuel gauge. The capacitor on the cluster will now be out of the circuit. Just splice its' wire into the "12v" source and it will be back in if you want. My car does not have one and all works ok. It may be needed if an alternator whine is heard through the radio. It doesn't on my car. Anyway, check out the diagram.

If it seems too much hassle for DIY, I could build and ship you one within the U.S. for $24 total.

Just don't forget that the heat sink is "live",it will short if grounded. If it does, it will just heat up the reg and eventually burn it up. I tested this for a few minutes and it did not burn up, but worked fine afterward. Did not want to be leading anyone on a path toward fire hazard! Make sure everything is insulated well and away from the wiper linkage after instillation.

When the instrumentation for our 60s-70s MoPars was designed, electromechanical devices were still far less expensive than semiconductor devices. That is why mechanical voltage regulators were used. Today, we can buy a semiconductor device for pennies (I remember paying DOLLARS for what is now a crude transistor). It makes no sense to stay with a mechanical regulator for your dash gauges, especially when you've updated to the MoPar Performance electronic alternator voltage regulator. To my knowledge, no one (yet) manufactures a retrofit regulator for the instrument clusters. But, with modern integrated circuits, it's relatively easy to fabricate one for yourself!

Before getting into the modern era, it might help to understand how the old type worked. There were two physical versions used on MoPars (they work identically). The A-body version was part of the fuel gauge; the others used a separate unit that plugged into the instrument cluster's printed circuit board.

The nominal 12 volts of the car's charging system is regulated down to (approximately) 5 volts by a thermal "bimetallic" regulator, similar to that used in a home heating system thermostat except that, in this case, the bimetallic strip is heated by a nichrome (nickel-chromium) wire element. As the heater element heats up, the bimetallic strip bends. When it bends enough, it opens a set of contacts - interrupting the output (and heater) current. The bimetallic strip then cools and closes the contacts, beginning a new cycle. The up-and-down voltage variations are smoothed by a capacitor (condenser) connected to the output. Over time, the contacts wear, and the heating element can go open. This is when your temperature, fuel, and oil pressure gauges stop working. Even when they are working, they tend to fluctuate up-and-down. It was a crude system but, at the time, it was the best thing available.

The New Regulator

The new circuit...

LM317T Connection Diagram (front view)

	V OUT	R2
	3.61	510 ohms
	3.84	560 ohms
	4.12	620 ohms
	4.40	680 ohms
	4.72	750 ohms
	5.05	820 ohms
	5.46	910 ohms
	5.88	1000 ohms
	6.34	1100 ohms
	6.81	1200 ohms
	7.27	1300 ohms
	8.19	1500 ohms
	8.66	1600 ohms
	9.58	1800 ohms
	10.51	2000 ohms
	11.44	2200 ohms

Bill Of Materials

Building the circuit...

The National Semiconductor data book specifies 240 ohms for R1 but that is not as easy to come by as a 270 ohm resistor so, the chart (above) shows the calculated output voltage based on the latter. If you'd like to be able to have a variable rather than a "selected" voltage adjustment, you can use (say) a 510 ohm resistor in series with a 1000 ohm potentiometer in place of R2. That will give you an adjustment range of 3.61 to about 8.2 volts. It's only a few pennies more.

IMPORTANT NOTES:

How it works:

Summary