1990 Nissan Hardbody ECU Ground Points

Hello,

We just purchased a 1990 Nissan Hardbody and it has issues with not starting after running for awhile (no set amounts of time, and seems to be fine as long as it IS running - however when you turn it off it won't start for random amounts of time from 12 hours to a few days). I have been assigned the task of finding out where the ECU grounds are so that we can check those and I keep hitting deadends. Can you direct me to where I might find a diagram that will show me these points?

Thanks so much!