Might have a manual for that truck, not sure, I'll have to check tomorrow.

As far as your issue, I would check the ground as suggested. Check where it actually grounds to the truck, make sure there is no corrosion, use a wire brush to clean the mating surfaces. I really doubt that is your issue but it's worth a shot.

Wish you lived closer, I'd love to take a crack at that one.

If you are looking for a manual I would certainly recommend online, anywhere from Amazon, eBay to Barnes and Noble. If you have to buy it in a store, try a book store, that's where I bought my almost useless Chilton's manual.

Oh and by the way, how many quarts of oil does a 72' Datsun take?