(ET) Most insane ground fault ever...

[Chris Zach <czach computer org>]

This is going to go down in history as the most insane grund fault ever...

E20-AA type tractor. For purposes of this discussion, the headlight 
wires are disconnected.

Here's the symptoms:

If I unplug the common wire to battery from the lift, the tractor works. 
However if I toggle the lift switch up or down, the field weakening 
relay closes with a *click*

If I plug in the lift to the midpoint of the pack (18 volts), the lift 
will go up and down. However the tractor is pulling current thru that 
wire to power the tractor field with 18 volts and the cc relay with 18 
volts (not enough to pull it in).

If I move the lift wire towards the + terminals, the lift gets weaker. 
However the current draw increases, and at around 30 volts the field 
weakening relay closes with a *click*. At 36 volts there is no lift, 
relay closes, full field on tractor motor.

If I move the wire towards the battery - terminal, the lift gets way 
stronger fast. I don't want to go that way too far, as the lift will 
burn out.

All of the above only happens when the motor field is connected. For a 
bonus, the drawing of current happens even when the tractor's main 
disconnect is *OFF*

What the HECK is happening?

Chris