Jd 4020 light problem

Ray

Well-known Member
I have a 1966 model 4020 diesel with the 24 volt charging system.The lights worked fine a few weeks ago.Now the inside fender lights and the rear light don't work.The outside lights work fine.I pulled the yellow wire off the back of the light switch that controls the inside lights,jumped voltage from the negative hot post of the battery and the lights work.The spade on the back of the light switch is hot,but when I plug the yellow wire back up the voltage goes away.I touched a test light to the bottom of the spade,the light comes on.When I plug the yellow wire in,the light goes out.I replaced the switch,but it didn't help.There are two relays below the switch.If I put voltage to the lower one the lights will work also.I've checked the battery ground ,positive to frame.It looks like a grounding issue to me,but I don't know where else to look.
 

Does tractor have the 2 circuit breakers on a plate mounted on starter? If so does both the brown & blue wires in wiring harness attached to these circuit breakers have 12 volts on each wire?
 
in archives there is home made wiring diagramn for 4010 that was helpful when working on neighbors lights on 24 volt system. might help
 
No circuit breakers on the starter.Two wires there hook together at a connector.The only circuit breakers i saw were two below the light switch.
 
The brown & blue wires at the starter are the batt A & batt B wires on the ign & light switches. Check them for voltage at the light switch.
 
The blue and brown wires at the starter are double wires.A&B at the light switch are hot when the key is turned on.
 
Go ahead and fight with it for a few weeks then change it over to 12 volts,, life will get better...
 
I will even add a third yes to changing it to 12 volt. He does not have a breaker kit on the starter so if he messes long enough he will get to rewire the whole tractor when the wiring shorts out and makes a whole bunch of smoke from burning wires. Do not ask how I learned this:>) Tom
 

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