88 Montero, 5-speed

Interesting combination here...

My left rear turn signal/brake light unit isn't working. However, the bulbs in that unit do work when I engage the hazard switch. I've swapped out the turn signal flasher. I've tested the unit with new bulbs. All fuses look good. Both turn signal indicators on the dash work fine. And I've swapped out the hazard switch (although the brake lights don't go through the hazard switch). No change. All the lights that did work before (both front and right rear) still work, but that left rear unit only works with the hazard switch.

Ah, but before you say it's the black wire, sportsfans, the tail lights (running lights) do work on both sides (tail lights use that same black wire for ground). Also, the backup lights do work on both sides (although I haven't found them on the wiring diagram).

And it can't be that the GL wire is open, because the hazards use the same wire (hazards work).

I haven't yet thrown a meter on it because I'm tied up taking care of some other things, but I'll be shootin' wires this afternoon or evening.

Any thoughts or suggestions?

I was having the same symptoms on my 88. I had running lights but no turn signals or brake lights. Here is a pic of my 89 under the dash just above the driverside kick plate.



My 88 didnt have the black box in it when I got it (and still doesn't). The plug to it was just sitting there dangling. I had no idea what the box did or if it even had anything to do with the lights. After I chased the wiring down and couldnt find a reason why it was doing what it was, I plugged a regular flasher into it and they worked. I'm not saying thats what your problem is but its worth a shot. HTH.

Thanks. That's the flasher. I first replaced mine with a spare I had, then with a brand new generic flasher. No change in symptoms other than the brand new flasher works better (it's a little faster).

If neither of my rear light units worked, or if the running lights didn't work either, or if the brakes worked but the turn signal didn't, it would be easier to troubleshoot. This combination of results has got me scratching my head. <img src="/forums/images/graemlins/confused.gif" alt="" />

Check for burnt wires. 1 rear assembly with a burnt wire will knock out the whole system. I had that happen once before.

Had an opportunity to troubleshoot some more tonight and now what's happening doesn't make sense.

First of all, I can't use the wiring schematic in the aftermarket manual I have because there are fewer wires actually on each of the connectors than are reflected in the book.

I started at the left/rear connector and metered all the wires (four of them) on the vehicle-side of the connector. All wire combinations check good and match what's occurring at the right/rear connector. If I take the left/rear unit and plug it into the right/rear connector, it works fine. If I take the right/rear unit and plug it into the left/rear connector, it doesn't work either on that side. The left/rear vehicle-side connector visually looks to be in good shape and is definitely clean enough for any good connection. But connecting either unit into that left/rear connector gives me no stop light and no turn signal on that left/rear side.

WTF!?!?

I'll try patching a new test lead from each wire to the unit tomorrow after I purchase them...what I have that's appropriate is also working intermittently due to a break internally in one of the test leads. Fortunately, my meter has good leads, but unfortunately, I can't use them for bypass-testing.

Have you added anything new to your rig in the past year that was installed by some wiring? When I mounted my ARB compressor under the hood in my Gen I, I learned the hard way that I should have put a wiring loom around the wires next to it. It eventually rubbed through the insulation and shorted out some of my lighting wires making my HiBeam operate when the light switch was in the normal position and the low beams would operate when in the HiBeam position.

Trailer wiring, perhaps?

John B.

Not in the last couple years. If I went back about 6 years, though, there's a bunch of stuff. <img src="/forums/images/graemlins/frown.gif" alt="" />



Perhaps. I removed the existing trailer wiring a couple years ago.

The thing that's blowing my mind, though, is that I am getting good readings back at the connector and the combination light unit works fine if I plug it into the R/H side. <img src="/forums/images/graemlins/confused.gif" alt="" />

Do you want me to scan and send you some diagrams from my '89 factory manual?

One thing that I can think of is that there may be an insulation break down that only appears when you put a load to the wiring. Voltage passes OK to the meter because there is no current draw, but as soon as you plug in a resistive load, the faulty insulation shorts to ground. I've seen it happen before and is a [censored] to deal with when you don't know it's there. You can diagnose it easily if you can get your hands on a megger, though. Just isolate the wiring you're testing, apply the 500VDC to the wire and get the resistance reading. You'll burn up 12V components at first contact, though, if you don't isolate the wiring properly.

HTH

I've found my 87 FSM schematics and have ditched the Haynes manual. Yeah...they are distinctly different. <img src="/forums/images/graemlins/angry.gif" alt="" />

Looking at the FSM, I now see where the common denominators are and have shot the GL wire (which turns into the WL wire) from the back end all the way to mid-harness where it crosses forward at the base of the passenger door and still have the same issue. I'm going to jump past the remainder and go straight to the steering column.

The common denominators which would affect power delivery to both the left/rear turn signal and the left stop light, but NOT the right/rear turn signal and NOT the right stop light are:

- the GL/WL wire (+) which runs from the left/rear combo light unit connector (supplies power to both turn and stop lights) to the turn signal switch
- the B wire (-) section which runs from the left/rear combo light unit connector across the back to join with the B wire (-) on the right/rear side (both sides share a common ground)
- the turn signal switch

A single power source (supplying power to both left and right rear turn signals and stop lights) runs from the hazard switch to the turn signal switch, then breaks out into two power sources from there, one supplying the right/rear and one supplying the left/rear. If the problem was the hazard switch, then neither left nor right would work (but the right side does work).

I'll check the B wire (-) by borrowing the B wire on the right side to see if things work. If things do work, the left side B wire segment is bad. If they don't work, then odds are that the B wire on the left side is good. Then I'll patch a new wire from the turn signal to the back. If that's good, then the GL/WL wire (+) is bad. If it's still bad, then odds are that the GL/WL wire is good and the turn signal switch is bad.

I'm just glad that I'm seeing some sense in things now.