control card was corroded inside -poor thing probably sat outside for a winter. thanks for all the input though guys

brushes and contact tips are good. I'm going to undo the busbars and hinge the contactors open and check the switches under them. Cool idea to put hinges on these boards. Not worth investing in to this old truck though...

I would go about fixing it exactly the same way as Ed. There must be a problem with the contactors or motor brushes that you should be able to visually see. That is assuming that the contactor pulls in but there is no scr hum.

to get Ed's quote for a warrantied repair;
Rebuild or replace all the directional contactor tips, and also the "d" [as in dual motor contactor, most likely mounted in the middle between the 2 sets of directional contact assemblies] and confirm or replace all the drive motor brushes.
my W.A.G. as to what is happening;
either;
one of the "at rest" positions the contacts or not making good contact (this would be far more likely if the problem was related to one direction [forward or reverse] or the brushes are just barely "worn out" and the greater current at bypass (1A) is enough to complete a circuit through the drive motor.

no scr hum with left motor contactor dropped out -what is it missing?

OK, put it in forward and turn all the way left. That way the left motor will be shut off. Then try to travel. Does the contactor for the right motor click in? Is there any scr hum even though you say the motor is not running?

yes both directional contactors are pulling in and the scr's are humming away driving the lh motor but not the right. Once the 1A pulls in then the right motor takes off. How does a single osc-card run both sets of contactors? I would have engineered it with two...

this may be a dual motor (D) contactor problem, do you see the contactor that drops out as you turn the steer wheel "lock to lock" ?

Either the f or r contactor for the right motor must be pulled in for it to run, even in 1A. Is the left motor running ok in scr range? With the steer wheel straight, do the contactors for left and right motors both work?

Ok -drive wheels raised -rh motor does not run until the 1A contactor pulls in then motor works ok. So, the rh directional contactors do not seem to be getting any pulse. What would cause this?

I would suggest getting the drive wheels off the ground as you do the checks, it makes it much easier (and safer too) to tell if/which motor is running in "straight ahead" mode...

right contactor does not pull in ever. I'm going back there this afternoon to see if I can track down why. Any other thoughts before I get there? Thanks for your help folks.

If, when going forward, if shuts off when turning right, then it's the left motor that's not working. If it shuts off going left, then right motor is not working. Watch the 2 sets of forward and reverse contactors to see if they are functioning properly. When going straight, 2 of them should be energized and when turning one of the 2 should drop out.

start by checking the drive motor and it's brushes, then check the contact tips if the motor can be run with jumpers.