Electrical gremlins, already!

[Alex V.]

My '90 SporTruck is almost ready to be licensed, but I have an electrical/lighting issue that isn't making itself obvious:

 

Every exterior light works as it should except for the pass. parking light and marker light, and the driver's front blinker - aka, I have one front parking/marker light and one front blinker, but they're on opposite sides. The things I've checked/ruled out are:

 

Both bulbs are new and I've switched them side-to-side (rules out a faulty bulb)

Both flasher relays on the fuse box appear to be good - the hazard flashers work, and I've switched the relays around with no change in symptoms

I'm not sure about the faulty blinker (didn't get a definite reading on it with my multi-meter), but the terminal in the non-working parking light socket has over 11 volts going to it - seems like it should be lighting the bulb???

 

A friend suggested it's a ground issue, but it seems if a ground was the problem the light wouldn't burn at all, or more lights wouldn't work. I wiggled the bulbs in the sockets and pressed them down while the lights were on, but still nothing. There are still several things I need to check before I'm out of ideas, but is there anything MJ-specific I need to know to troubleshoot this problem comprehensively?

 

Thanks!

[DREDnot]

I'm going to have to assume that your 90 is the same as an 88 for this.

Find the c102(10 pins) connector behind the drivers side headlight.

Disconnect it and clean the contacts. Then check for continuity between the #5 pin(F) and the G103 ground on the drivers side inner fender.

Then check for continuity between the #5 pin(M) and the ground prong on both turn/marker sockets.

 

The 1988 electrical troubleshooting manual PDF shows you everything about the wiring loom including connector/ground locations and pinouts.

It is a must have.

[mvusse]

The socket might be bad as well.

 

If there's no ground, it should ground through the turn signal filament. Is your turn signal indicator on the dash lit when your lights are on?

 

11V measured by a volt meter doesn't mean much. If it's high impedance 11V then the voltage will drop to almost 0 with the relatively (compared to the meter) high current draw from a bulb. Measure the voltage with the bulb in there or use a test light instead of a multi meter.

[cruiser54]

I'm going to have to assume that your 90 is the same as an 88 for this.

Find the c102(10 pins) connector behind the drivers side headlight.

Disconnect it and clean the contacts. Then check for continuity between the #5 pin(F) and the G103 ground on the drivers side inner fender.

Then check for continuity between the #5 pin(M) and the ground prong on both turn/marker sockets.

 

The 1988 electrical troubleshooting manual PDF shows you everything about the wiring loom including connector/ground locations and pinouts.

It is a must have.

 

This^^. If it were mine, I would unplug and clean the 10 pin connector anyway, and remove the ground wires from the left inner fender and scrape the area clean and reinstall the wires tightly. It's only a sheet metal screw.

[Alex V.]

Thanks for the replies and suggestions, and sorry I've been so long in replying. With a little troubleshooting and investigating, I got all the lights on the Comanche fixed; the parking light was a ground issue (the small strip of metal that grounds against the bulb socket had rusted in half - made a new one of those) and the blinker was just a faulty connection where the pins go into the back of the socket. I tied up the other loose ends and it passed inspection on Monday, and all that's keeping me from driving it now is the bent driveshaft - it becomes noticeable at about 30 MPH and is pretty prominent at 55-60. I've located one at a salvage yard about 60 miles away, so if all goes well I should be driving it to work in a few days or so and slowly fixing the little 2.5's problems. (A manifold gasket, VC gasket, and fan belt will be some of the first things, then seeing what I can do about the blow-by and mild peck in the engine.) Judging by the amount of gas it's used in the 50 miles I've driven it close to home so far, I think it's doing very well on gas. :cheers:

 

More later!

[mvusse]

I wonder how long it took you to McGuyver the socket when a new one from the help section at Advance Auto Parts costs just a few bucks.