yes that is exactly right. the cable is still connected from the negative battery to the frame of the tractor. but apparently is not making a good ground. is just enough to get a good read but it drops to 0 on a load test.
so if you load test from bat positive to bat negative and it tests good.. but test from bat positive to chassis and it is -0-.. then the connection from bat to chassis is bad at one of the ends or the cable...yes that is exactly right. the cable is still connected from the negative battery to the frame of the tractor. but apparently is not making a good ground. is just enough to get a good read but it drops to 0 on a load test.