Dash Light Head-Scratcher...

Here's one that's got me stonkered - for some reason, my dash lights have decided to "reverse" operation. When the key is ON and the light switch is OFF, I have dashboard lighting. Key ON lights ON, no dash lights.

1988/4.0/DIY Headlamp Harness (in place two years.) No visible defects in wiring (OEM or added) and new-"ish" headlamp switch (read: I put it in my 87 a couple months before I took it down and then moved it over last night - switch has NO crud on it.)

Switch function checked with meter, seems OK. I decided to change the switch because A) it was original and B) I was having half-running lights on with the old switch OFF key ON. Changing the switch corrected the running light issue (right rear was ON, rest were OFF.)

I know I'm going to have to dig into this one, but I was just wondering if anyone else has hit their head on this one and had some ideas before I got into things...

5-90

by any chance do you have an aftermarket radio that may be tapped into the dash light circuit (orange wire)?

Might want to check that you didn't dislodge headlamp delay module, illumination relay, or chime module.

Are your entry courtesy lights working correctly?

Look for something else that shares that circuit in some way, having a bad ground, so that instead of going to ground in the normal path, it goes back through the dash lights. The radio, suggested above, is a good place to start looking.

Yeah - I've already started going over my FSM wiring diagrams...

UPDATE -
I removed the switch to check it, and examinated the connexion while I had it torn apart. Now, the panel lights are on whenever the key is ON, irrespective of headlamp switch position. ?!?

I may just say "Hang the whole mess" and put in a batch of toggle switches and use them instead...

5-90

Grounds are always suspect. Under the dash far left, near the kick panel (under the headlight switch), there is a ground cluster, that often comes loose (last screw to the left bottom, very near the drivers side, floor courtesy light). While I´ve got that light in mind, check the wires haven´t been burnt or melted by the light.
The harness under the carpet, drivers side, often has green splices and frayed wires, usually affects the dome and courtesy light circuit.
Easy to put a screw through the harness under the drivers side door sill, kick panel.
If you have the trailer harness, try unpluging the relays (behind the panel, behind the spare), or just pull the fuse under the drivers side kick panel.
Check the harness, by the headlight switch for cuts.
Pull the instrument (lighting) fuse and see what happens.
Good luck.

Well, this after-noon was a runabout, but I'm all settled down (and fed!) now, so here's some more information...

1988 XJ Laredo, homebrew headlamp harness (two years,) aftermarket stereo (stolen a couple months ago, replaced a month ago,) some additional power distribution goodies.

Headlamp harness has been in place long enough that I know it hasn't been causing trouble, and only connects to OEM wiring at right headlamp connector

Headlamp switch replaced yesterday - two symptoms:
1) Panel lighting flicker on and off when engine started (which runs thru key and dashboard switch - done about two years ago.)
2) Running lights (NOT stop/tail, but 2d red light down) on right side ON with key ON and switch OFF.

Replacing headlamp switch cured running light issue, panel flicker. Caused reversal of panel light operation.

Switch relatively new, but pulled and checked anyhow. Checked with DMM and FSM for proper operation, just ducky. Terminal for harness clean and okeh. Reassembled for after-noon's running about.

Now - dash lights always on, dimmer no worky (no big deal there - I never used the damn thing anyhow) and headlamp switch operation otherwise normal. All other lights off until commanded.

The previous stereo head unit was "harvested" without molesting the wiring - I planned it that way. Not so much for the head unit being stolen, but because I'd planned on getting something better eventually, and the entire harness could be pulled without cutting anything (I'm unpleasant, I'm not stupid...)

All underdash wiring and grounds visibly fine. No sign of mechanical interference.

XJ came with 4- and 7-wire trailer sockets, but I removed the wiring until I could do a better job of installation.

There are no screws or anything puncturing the front-to-back harness - I had to get into it to put the amplifier in (which is still unmolested) and much earlier when I installed the cargo bay powerpoints.

I'm still tempted to just fab up a switch panel to replace the center vent and wire everything thru there, using an extension harness and relays. Probably will, but this is just too strange to not tell you guys about...

5-90

Two things I can think of, most important is "wierd shit = bad ground". Second, make sure you don't have a one filament bulb stuffed into a two filament socket. Like a park lamp bulb stuffed into a park and turn socket.

Nope - all of my bulbs are correct and in clean sockets (I'm pretty careful about stuff like that...)

The odd part is that this is all going on with no noticable defect anywhere. All my grounds are good - believe me, I know what can happen when you got a shonky ground!

I'm still wondering about this, but it's been shifted to "low-priority item" since I can now see my panel at night...

5-90

check the braided ground strap that goes from the firewall to the cyl head bolt, it can be loose or broken.

I got rid of that a long time ago - replaced it with 0 gage welder cable! I never did like those braided grounds...

5-90

well, you might want to check it anyway. sometimes it comes loose enough to cause weird problems.

The other thing that occurs to me is that if it's a home-brew harness, did a pair of connections get reversed somewhere? Are you using individual connectors at the headlight switch instead of a single plug? If you're "sure" you did it right, you check it seven times and not realize it's wrong until the eighth.

Couple of things popping into mind, been awhile since I´ve messed with the headlight switch.
Do the dashlights dim? Is the resistor coil still in one piece? (probably gonna need a mirror and flashlight) Is the resistor wire, burning through the harness? Seem to remember, being able to get the plug on wrong, for the switch in the back, can´t remember exactly what it was, with the connectors, just remember it´s something to pay attention to (like I said it´s been awhile). Almost impossible to see unless you pull the instrument cluster.
Sounds really simple, but it´s possible to get function (somewhat) without the knob and rod being all the way in! Have to be carefull if the rod isn´t lined up with the resistor wheel this can break something. But have had to thump the knob pretty hard, inword to get it to seat, all the way. Can´t remember the exact symptoms, but the knob/rod not being in all the way, makes for some strange functions. Looks like it is in all the way, but it´s not, seats in farther than it appears at first glance.
I tossed the last bad switch I replaced, if you still have your old switch, take a close look and see if it would be possible to get the switch contacts and resistor wheel out of sync. Check and make sure the knob and rod is seated all the way to the stop!
Check the ground behind the windshield washer bottle.
There are a couple of resistors built into various harnesses in a couple of spots, worth a close look at the wiring diagram to see if there isn´t one someplace in the headlight circuit.
Unplug the timer for your headlights, could be a source of power into the circuit, where it´s not supposed to be. Same with the trailer relays. The courtesy light bundle under the drivers side carpet.
The radio wiring is strange (non standard). Blu and orange/white wire for the panel illumintaion, is strange, blue is for daylight illum and orange and white for nighttime (dimmed) illum. Red and tan is for the memory circuit. Would be easy to get a circuit crossover at the radio.

Well, I did check the ground lead anyhow (not a thing wrong with it - all primary grounds in good condition.) I'm looking at the switch that I took out, and the connector is not reversible, so that idea's out.

The rheostat coil on both switches is in good condition, and show similar resistances. The dimmer worked until the switch change, but like I said I don't care about that - I usualy have it cranked full up anyhow.

I didn't see any sort of bridging or contamination on the harness socket, on either side. Thing was barely dirty...

The headlamp harness is still as I set it up - two years ago. No problems there to cause issues like this. The relay trigger signals are taken using .250" spade lugs inserted into the right headlamp socket. The relays and fuzes added for the harness are in good condition.

The stereo wiring is/was correct when I installed the new head unit, but I've nowhere to go to-morrow so I'll probably dig in and check it out to be certain.

I have done electrical mods, but most have been sourced from distribution points added for the purpose. I do try to leave the OEM wiring alone unless I'm going to tear it all to bits, simply to keep track of changes. Naturally, I have a notebook for each XJ to track modifications (I'm not stupid - I've dealt with sorting out other people's "custom" work before...)

This afternoon, I had no dash lights at all. This evening, they were back. Damn...

5-90

What year did you say your Jeep was? Does yours have a fuse panel behind the pass side kick panel like my '98? A long time ago I was having the strangest problem with mine. I really wish I could remember the problem exactly because it was strange as hell but I cannot. Anyway the problem wound up being that windshield washer solvent was somehow leaking into the Jeep and running into that fuse panel. Over time it corroded and caused a current path that was turning on stuff that should have been off. It seemed strange to me that enough current could flow to actually turn things on hard, if you know what I mean, but it did.

With a meter and the FSM you should be able to track it down. The lights not dimming are a big deal if the HL switch is actually good. If you really want some help with this I can look at the FSM and take a closer look at your description. I don't think I would go the toggle switch route just yet, but that's just me. Problem with modding wiring is if you don't doccument it well it can be a big problem later when you run into a problem like this but have no documentation to help you out. Plus I would want everything straightend out BEFORE I started modding the wiring.

B-loose

B-loose

Sort of new to the Jeep game, but not to electrical circuits. Sounds as if you might have a live circuit, that is, power provided to the light panel and a ground switched to turn it on. You may have an intermittent ground contact to the ground on the panel, causing to to turn on. Check mounting screws, washers, wires, ect or anything that might provide an unwanted ground connection.

The dark blue wire to the parking light, marker light, licsense plate light, clock, ?radio and others is tied to the instr circuit illum before the resistor (instr light dimmer). If there is any voltage on a Blue wire circuit with the headlight switch off, it´s probably crossed downstream from the switch someplace. But if the instr lights don´t dim, this is probably not the problem, the two circuits appear to tie together before the variable resistor (dimmer knob). Could your relays be full of water or corroded internally?
The instrument LPS fuse appears to be after the resistor, if the instr lights still illuminate with the instr LPS fuse out, it´s probably in the cluster or a ground. Pull a couple of fuses and see if things change. Radio fuse, cigar lighter fuse etc.
Disconnecting the fusible link to the headlight switch (GRN), might also help to narrow it down some.