It looks like we have discovered another difference between Chev and GMC. Electrical is section 7 in GMC Maintenance and pages 302-305 are devoted to wiring schematics for 1955-1959, 100 series to 500 series. They all use a 3 terminal ignition switch. I was twisting wrenches when these were new and GMC mechanics always unhooked the wire at the starter when they were looking for the timing mark. I was not aware that Chev used a different switch. My uncle sold GMC's and we had all GMC's until I bought a cab over International in 1968 and my truck fleet is still all International. I bought my first Chev pickup on 2003 when my cousin started selling Chev in addition to GMC but I don't fix anything on them.
