Friends,
I am fed up with these horrid inaccurate wiring diagrams, Hanes and Chilton manuals are my primary complaint now.

SO! Where do I find an accurate electrical schematic for a '90 GMC Sierra 2WD 1/2 ton with a V6 and manual tranny and a '91 with a 5.7L TBI (K) and a THM700 tranny.

There seems to be part of the electrical harnesses from both in my truck. The engine, tranny, & electrical harness seem to come from the '91, except the part of the harness in the engine compartment that come out of the firewall on the drivers side and feeds some of the engine, the grill area and rear of the truck, that seems to be original.

Both halves of the coupling at the firewall are the same and connect but the wires are not in the same locations and thus not connecting to the proper things on the other side of the firewall.
Sincerely Jon

 

Personally I like Alldata's wiring diagrams. But I've never had an issue using Haynes diagrams or ChiltonPro (the online chilton) diagrams before. It's always turned out to be exactly what the diagram says it should be.