Hello!
I have 1977 C20 that I've been working on getting back on the road and It's in need of a new Wire harness. It's missing wires and has cuts and exposed wires everywhere. I've been tossing around the idea of building a whole new one from scratch or just buying a new one. I've found a few from Brothers, Summit Racing, American Autowire, and so on... But I stumbled across a 1978 C30 with a 454. The guy is offering a great deal on the whole wiring harness Cab, engine, and body wiring, the whole sha-bang. But I'm not sure if a '78 454 harness is compatible with my '77 C20 with a 350. If any one knows for sure or if it's even close to being usable, it would be appreciated!
Thanks!
-Cliff

 

are you planning on using the 78 cab? if so theres nothing to worry about. if not the only issue is the bulkhead connector and even then i dont there there was any change till the 80s (81) but the color code for the wires is pretty much the same.

you can find the 73-87 wiring diagrams Here if you check here the 77-80s even use the same diagrams

and the 73-87 truck manuals Here

 

also the cluster pin out you can find Here