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GM uses a Pulse modulated signal to run the dash lights. The shorter the pulse the brighter the lights. The radio has a " Booster" -- amp, or "ac elecrtonic dimmer" for the pulses comming from the main chassie, controls- this boosts that to feed the radio back lights, and the AC panel light dimmer controls. This keeps the addtional loads off of the chassie feed, and puts it on the radio circuit fusing. Well,when I get a unit built of off the bench to make up for the factory radio messing I'll post it. Have to get the pulse feed over to the AC controls without loading it up the chassie leg.
Rusty Nut