My low beams and fog lamps aren't receiving power. Or, more correctly, they're receiving power but not ground (as the wiring in our cars is apparently negative switched). I checked the fuses and can't find a culprit. (There doesn't even seem to be one single fuse that controls both low beams and fogs.) I searched the JJTIS but can't find what I need to diagnose the issue. I'm assuming it's a relay, but can't seem to find the info I need in the owner's manual.

In other words, I'm not sure which relay to check or how I'd even know if a relay wasn't working.

 

Anyone got an idea?

 

JTIS Electrical Guide section 8 probably fig 08.1

 

Cool, I'll check that out and report my findings.

 

I didn't realize there was a separate "electrical guide" to the JTIS. Thanks for pointing that out JagV8.

I confirmed the fog lamps DO work, I just forgot for cars, you can't run the high beams and fog lamps at the same time.

In looking at the electrical diagram, it shows there is no relay or fuse controlling non-HID headlights.

I went out and verified that the high and low beams are negative switched. Both the high and low beams receive constant power regardless of their switched state. The switching end clearly is on the negative side.

The high beams work perfectly, but the low beams don't. I've already confirmed the low beams do work when connected to an independent ground. I suspect it could be a damaged connection of the wires leading from the low beam connection (there was a lot of stress on the wires getting the bulb connector off in the first place). But at this point, I don't know how I can proceed.

What do you guys think might be the issue?

 

To a fair extent you can figure out the routing of the harnesses, partly from JTIS / that Guide and partly by brainwork. In case you figure they go via the thick harness behind the front bumper / above wheel arch, that harness has been known to have corrosion problems. See what you think...

 

Ok, I can do that. But one thing I'm not used to is working with negative-switched electronics. I know how to test positive-switched electronics, but how do I for negative?

For positive, I connect my light tester to a known working ground and touch the positive end to the positive connection I'm trying to test. If it lights up, power; if it doesn't, no power. What would I do for this situation? Connect the negative of the light tester to the ground I'm trying to test out and touch the positive of the light tester to a known working positive source; if the ground gets switched on, the light should light up; if not, no light. Will that work, is that the way I should test out this ground-switched system?

 

I caution against using test lights with modern electronics as you can easily fry them. DVOM please.

 

Yeah, you got a good point, guess I gotta' bust my outta' the closet or wherever mine's hidin' at.