Thanks for the info will check.
Regards
not sure if your serial number sets on the microcommand II
if it is... like somebody said.
I´ll put my money on : wiring circuit of field shunt fuse,since,for a truck that age, and taking in account the amount of current the motor field takes. contact points tends to corrode.
if not, a will suggest connectors at logic card. and the bad..
logic card itself.
Check power relay. or other power relay. measure coil. Old power realy 130 Ohmios, news 30 Ohmios.
Sorry for me English. But check you mail for more information.