1978 Gmc Fuse Block Diagram - gm-trucks Jun 14, 2008Just bought a 1978 GMC 6500 single axle truck to replace a 1958 Mercury single axle truck. The truck runs good, and though it needs a little work, the price was right on it. Before I take it to get saftied, I need to get all of the lights working on it. After a Hello. I need to find a fusebox diagram 1978 chevy van - Fixya wwwa›Forum›Cars & Trucks›Chevrolet›G20Jan 28, 2010Hello. I need to find a diagram that shows what the fuse box layout is in a 1978 chevrolet one ton van. The labels on the fusebox are illegible and I need to find out which is which to try and diagnose multiple electrical problems.