I'd start by seperating the firewall bulkhead halves & cleaning the brass terminals. A small metal bristle brush for the male ones and a spare male one (new is NAPA 725147) for the female ones. Brush on Koppr coat (sp) if desired. Then with your meter on OHMs I'd see if you have continuity between the 2 main in/out wires at the bulkhead, the one in past the fusible link & the one out to the alt (black on that one I believe) & as you know it's always a good idea to unhook a batt cable before switching the meter to OHMs.