Ammeter to Voltmeter...who does it?

IVR is instrument voltage regulator. The gages run at 5.5 6.0 volts. Leftovers from 6v electrical systems. When it all went to 12v the car companies came up w a tungsten tipped vibrating point type regulator to bring the 12v down to 5.5-6.0 volts. As it gets old if the points stick open typically your oil press, fuel, and water temp gage drop off, if it sticks closed they peg. On dodges and chryslers its a little box w 3 prongs on it clipped to the gage circuit board. One prong is ground, ine is 12v in, the other is 6v out. Plymouths for some reason have the damn thing mounted in the fuel gage. This requires some surgery to disable the regulator while leaving the gage working.

Back then a solid state semiconductor was expensive so the vibrating points was the way to go. Now a days a NTE 960 semiconductor chip does the same job for about $1.50 plus a small capacitor as a shock absorber. For about $5 you can make one.

Forget the ammeter. The whole point of a volt conversion is to take the amp load off the bulkhead connector.