Need help on bulkhead wiring

One common problem is that when the bulkhead connectors are pushed on, the female terminals push back in the housing, i.e. the little side latch doesn't hold it. You can see that under-dash w/ a flashlight. Only one of the 3 connectors is for engine functions. The others are "headlight" and "wiper", though those aren't exact definitions. My 1965 is simpler (2 connectors) since the wiper motor is in the cabin and the thick ALT & BAT feed-thrus are on special buss-bars. Since only dealing with the single yellow wire, it should be fairly straight-forward. Just tell him to take a breath and not get jiggy. Also, insure the black lead is on a solid ground same as BATT- or just run a long jumper wire there. Insure the starter relay's case is at BATT- (within 0.1 V), and stays there as you try to crank. Bad grounds are a problem in anything electrical.