I am working on 1965 JD 4020 with the 24 volt system just trying to get fuel guage to work then maybe check out the lights but boy oh boy its driving me crazy. The tractor has original wiring harness that is in very good condition, but when I put circuit tester point on platform and scratch it and other end attached to the positive post on RH battery the test lite lites up omg. I do have a JD service manual studying the wiring harness but still now power to fuel guage and I did put on a new ground wire from the LH battery so I am thinking I need to remove the operators platform to see what is rubbing underneath. Also sometimes I have power coming to the 2 circuit beakers mounted on the switch panel then next time I do not. The tractor has sat about 5 years and I am just trying to get it ready for use this summer .