Instrument cluster regulator
No you get resistors to simulate the low, the mid scale, and hi scale ends of the gauges, Dana67 already posted. Or if you have a rheostat or spare gas sender, move it to those resistances with your ohmeter and then see where each gauge goes. All three gauges should indicate the same (one at a time) with the same resistance tied to the sender post
This is a 3rd party gauge tester from "back then" and Chrysler made a similar one. They were a switchbox containing three resistors
No you get resistors to simulate the low, the mid scale, and hi scale ends of the gauges, Dana67 already posted. Or if you have a rheostat or spare gas sender, move it to those resistances with your ohmeter and then see where each gauge goes. All three gauges should indicate the same (one at a time) with the same resistance tied to the sender post
This is a 3rd party gauge tester from "back then" and Chrysler made a similar one. They were a switchbox containing three resistors