Hi there. I have been working on a cat F35 which does not have any plates with serial number or anything. Its the old F35 3 wheeler with twin motors. The problem I am having is:

Power up ok and if left on after a few minutes it just chatters the line contactor in and out until it eventually drops out the line and needs to be re set by the key switch in order for it to work again. If you turn it on and drive the truck or use the hydraulics it does the same thing, works for a bit then chatters the line until drops out again.

Its losing its negative to the line coil, however when I disconnect the negative feed off the coil and power the key on, the negative remains. Its only when the system is powered up with the line contactor coil connected this problem happens.

I had thought that if it was a logic fault then surely it would lose the negative supply with or without the line contactor coil connected, but not sure now as everything points toward this logic card.

I powered up the coil with a direct pos and neg to see if the coil was breaking down, but that seems to be ok. The coil remains powered up.

The negative into the card at the various pins remain correct. Can anyone help or has anyone come accross a similar problem. Have currently removed the logic and having it tested but would appreciate any comments.