Paul - I know you probably need information on the transmission wiring more than on the engine, but I can supply what I've decoded for the 4JB1. Based on my experience, I'd guess that most will match between what I've got and the 4JG2 (if the gas truck colors match the diesel wires, diesel-to-diesel should be a snap!).

I will dig my notes up tomorrow and post the colors if you'd like. School is finally out, so I have some time on my hands.

1988 Isuzu Trooper LS
2.8l Isuzu 4JB1-TC intercooled turbo diesel
www.dieseltrooper.blogspot.com