[GM72K10]

Awesome find. I bought an 86 very similar except that the body was removed before I got it.
Wound up replacing the engine compartment harness (easiest route)
I take it you are keeping it as is and can't get it running.
Glow Plug controller was in need of replacement among other things on mine. I still can't get the horn to work either. A few bad grounds and some shorts. Had to rewire the headlight switch wiring also.
My plan of attack would to be disconnect everything and start over .
Just my two cents. I used the stock K30 K31003 diesel wiring harness diagram, it helped enough to get mine running again.
It is quite different from the cucv wiring harness I might ad.
Good Luck.Posting pictures of your engine compartment compared to mine and my truck when I got it. You have a much better truck to start with and I paid the same price!