1977?
The only wiring you should have is for your reverse lights on the side of the tranny. If everything lines up, you will be needing to see if your fork is moving when applying the clutch. If it is, you might want to take the tranny down and make sure everything is assembled correctly. I tend to appreciate the old chilton books. Find a chilton for light truck and and van for your particular year. If not a chilton, then get an overhaul manual.