Totally Stumped.

[aces74]

1998 Mercury Mountaineer, 5.0L

Dash lights have completely gone out, as have the tail lights. Also, the O/D indicator does not light up (nor does OD kick off) when the O/D button is pushed.

Replaced the Dash Dimmer switch. Nothing.
Replaced Multifunction switch. No dice.

All fuses checked, and there appear to be no wires damaged, etc.

The weird thing is this; When we bought it 6 months ago, the O/D indicator never worked. Then about 6 weeks ago, the tail lamps (parking lamps) stopped working. Same day as the dash lights went.

Then one day all of a sudden, the O/D indicator light (and subsequently, O/D) started working. The tail lamps worked also. This was about 3 weeks ago.

Last weekend, everything stopped working again, and I haven't been able to get it back since.

 

[manaen]

sounds like you have a bad connector, you need a wiring diagram and start to check all the main connectors in your harness. Could just be a loose connection, or maybe the connector is oxidized. I always use dielectric grease (tuneup grease) on all electrical connectors. CO contact cleaner will help to blow off the oxidation. Other than that I cannot help since I don't have the specific diagram for your truck...


Good luck

 

[yodicoyote]

check your fuse pannel. it sounds like you might have a bad circut board, well at least that what is sounds like.

 

[aces74]

Little bit of an update, something I *forgot* to mention (and didn't think much of at the time)

There was a wire, running from the fuse box under the hood (wedged in with a fuse, I can't remember WHICH one) that ran to the back, up into the driver side taillight wiring.

It was fraying, and coming apart at the multiple splices in it along the length under the truck, and silly me, I assumed it was for something that was ghetto-rigged into the truck from before. (aka the DVD player that was half hooked up, but with a bad player, or the trailer wiring that is cut in half... *facepalm*)

Now I'm wondering if maybe it was a bypass for a bad wire in the harness or something, just running direct power to the taillights for when the circuit opens.

Anyone know which under-hoof fuse would be the one?

Obviously, I'll get out there and test the circuit tomorrow, but if anyone knows for certain which fuse it would be (if this, in fact, the case) to directly wire up to the tail lights.

Would explain the erratic activation (and subsequent lack of activation after I removed it) for the lights.

Not sure about the dash lights, OD indicator light.... might all be related.

 

[Bill Kemp]

We have had trailer light harness problems. The harness gets shorted out and that affects the tail lights. When the tail lights go out so do the dash lights. Sort of a warning feature. Dont know about the OD light though.
I would concentrate on the tail lights and the trailer harness...

 

[aces74]

Ok, little update. The wire I removed was the old ghetto-rig that the previous owner had going. Fuse #15 in the fusebox under the hood, wired into it and directly to the white wire on the driver side taillight.

So I replaced the wire, wired it up so at least I've got taillights. BUT a couple things I did notice.... in the fusebox inside the dash, fuses 32,33 and 28 (I believe - it's the radio GEM) were dead. Couldn't get them to light with a circuit tester, no matter what I turned on...

So I'm assuming there's a legitimate problem somewhere that I'd like to track down, but for the time being, truck operation is normal...

 

[High_Order1]

You need to start looking at your grounds, as well.

Shawn