I'm not butting in, but if you go to a manual controller, you can eliminate the controller completely and just use the solenoid from it. I have two 6 Volt batteries and power the GP's with 6 volts (design voltage for them) from one of the batteries to the solenoid, for about 35 -45 seconds in normal temps, maybe 60 below freezing. The button in the cab is the ground signal to the solenoid. Advantages to this is they don't cycle every start, extending life by double. They don't swell up from overheating at 12 volts. ( the controllers job to cycle on/ off). And you can run a simple electrical system with the one wire into the cab for the button. I have run this with the stock harness for 29 years. Think manual glow plugs in an electric start D-7 from the 70's. Hold to Heat, and count seconds. In the pic, bottom center is the solenoid feeding the 6 volts thru to the GP's.
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