I am in need of a wiring schematic for the engine wiring harness.

Hi, I recently took a job for a customer putting a engine in his 1989 Chevrolet C2500. The job has been a nightmare from the word go. I have done engine swaps/replacements on this generation chevy/gmc pickups already 15 time but unfortunately somebody else pulled out the old engine and I also found out (after the fact) that it was removed more than a year ago. I now know why so long because whoever removed the old engine was to put it lightly, a hack and moron. OK to my issue when the old engine was removed they were not concerned with disconnecting the wiring and because of this generation truck's common issue of the old wiring becoming very brittle I have more than a few broken wires. I did not charge very much money to do the job due to trying to help a friend and do this customer (who is 81 years old) a favor and trying to say as money as possible. Does anyone happen to have a wiring diagram/schematic of the engine wiring harness/front of vehicle?? Your help would be EXTREMELY appreciated. Thanks in advance, Larry.