Greetings all !

just got my hands on my first Volvo, 1976 242. great condition with 140k.

I just finished replacing the blower motor. The car runs great but I have a perplexing intermittent electrical issue. Intermittently the car will shut down when I turn on the headlights.

I only drove the car for about 20 miles prior to getting into the blower motor so I am not sure If I caused the problem or it pre-existed.

Anyway, with the engine off and the IGN on I can hear the fuel pump activate when I turn on the headlight switch , with the engine running the car dies when I hit the hl switch.

the electrical is very basic on this car, I am thinking maybe a bad ground somewhere or possible bad Ign switch ?

Appreciate any insight.

 

something is fubar, thats for sure.

lets see... battery + goes to the 'positive terminal' (box where many red wires are connected together, probably on left fender under hood). one wire from the positive terminal goes to fuses 6,7,8 which are always powered. another wire from the positive terminal goes to the ignition switch, and pin 15 of the ignition switch is a blue-yellow wire to fuses 3,4,5 which are powered when ignition is ON (II) or START (III).

fuse 5 has a blue-red wire to relay 1, relay 1 pin 30 has a grey wire to relay 2 pin 86 (coil), relay 2 pin 30 gets power from fuse 7, and relay 2 pin 87 yellow wire powers the fuel pumps. if the switch in the K-Jet airflow meter is closed, relay 1 disconnects the power to relay 2, shutting off the fuel pumps.

the headlight circuits shouldn't be anywheres NEAR this stuff.

I think I'd take a volt meter, check the power on fuse 5 and play with the headlight switch, it shouldnt' change. check the power on fuse 7 too, same thing, shouldn't change.

the headlights get their power on a blue wire from the positive terminal to the headlight 'step' relay, and a yellow wire from headlight switch pin 56, the step relay either powers pin 56a (high beams, 2 red wires directly to the two headlights), or pin 56b (low beams, a grey wire to the bulb-out failure sensor, which in turn has a blue wire to each headlight lowbeam). the stalk on the turnsignal grounds the step relay pin 31b via a brown wire, this causes the step relay to switch states. NOTHING there should go anywhere NEAR the ignition/fuel injection systems.

[this is all elucidated from the 1976 Greenbook wiring diagrams, volvo publication TP-11094-2]

 

Thanks for the info, this was or is a head scratcher. Finally able to at least isolate the problem. I was getting power feed back into the system causing the weirdness. I checked the continuity in all the dash grounds, found a black ground coming out of the harness on the bottom left side of the dash by the radio area, the ground wire ( I assume) had varying resistance and showed varying voltage with the IGN on.

I taped it off for now and the problem is gone. Not sure what is at the other end yet but all the exterior lights other than the back up lights are working.

Ill post when I get it figured out.