[Tx Jim]

Technically about the only thing that needs to be changed on wiring harness when changing from 24 volt to 12 volt is relocating brown wire on starter solenoid to the large top post together with blue wire. This is assuming batteries are attached correctly to give 12 volts & alternator is connected correctly. IIRC fuel gauge &/or sender need to be replaced for gauge to operate correctly.

 

[Tx Jim]

Did these tractors have a neutral switch in the start circuit? I did not see one in your diagram :unknown:

All JD 4020's came from factory with neutral start switch, Syncro-range trans had 1 NS switch & Powershift trans had 2 NS switches

 

[Tx Jim]

I don't think it would make much difference with both hooked to starter vs one and having the other daisy chained. Shouldn't matter at all unless your cables were in bad shape.

Anybody know if it is worth it to install a starting relay? The tractor has never had one and has always worked so not sure if it matters.

Thanks for the feedback.

Having both positive posts of battery attached to starter solenoid will give more cranking amps to starter. Only reason JD added a starter relay was to increase amps on yellow starter solenoid exciter wire. If ones tractor starts good then relay isn't required or needed.

 

[Tx Jim]

JohnnyQ
Welcome to GTT
Are you rewiring your tractor as 12 or 24 volt system?