Wiring Diagram 1993
http://67-72chevytrucks.com/vboard/showthread.php?t=465888&page=2
The wiring diagram is sectioned by areas. Easy to print but a pain to use.

It's not easy troubleshooting wiring harnesses with plugs and sockets.
Do not force a plug or socket to disconnect. They usually have a clip or retainer that needs to be pressed or guided.
Check areas first that are easiest to access.

Has anything electrical been added lately?
Has there been a recent damage or wreck that may have damaged wires?

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."