Did I mention I hate diesels!!!! Been working on a customer/friends 377 for a no-run condition now for at least 4-6 weeks, and finally have figured it out!!!!.. First I replaced the broken field coil with a new one, and that didn't help. Checked the wiring at least 6 times, all was correct. Put in a new armature, that didn't do anything. Kept getting a short, and some smoking.. After MANY attempts at correcting the problem, I noticed the field wires were touching the brass holder/sling,( they don't give you much room). Fixed that and the motor came to life..Ran perfect on the bench but wouldn't run at all on the lay-out. Took it out this morning and test ran it on my friends lay-out, same thing.It would run about 3 inches, then go into reverse, then forward.I saw it was a intermittent power loss causing the problem, and pulled off the sintered pick-up wheel on the powered truck and replaced it with a NOS steel wheel.....The sucker took off, ran 816' without any stops, put it in reverse, and it ran over 750'.... I believe I fixed it, after all those weeks.. Now I have to come up with some type of labor charge, I can't charge the guy what I actually have in it... Parts bill is easy, labor not so much.