Instrument cluster.

The instrument cluster lights (spdo, tach, etc.) do not illuminate, but the others (check engine, door ajar, etc.) do. I've just changed the bulbs, and that didn't work. The dimmer switch works for the dome lights, and there are no other problems. I've checked the fuses and they are all OK. Rigth now I have an LED taped above my steering wheel in order to drive at night. Any ideas as to what may be wrong?

Welcome to the forum!

What year is your Mountaineer? Do the other dash lights for the radio buttons, HVAC, etc. work?

-Rod

Forgot to mention that it is a '98. Everything else works just fine in the vehicle. Discovered that the dummy lights (check engine, O/D off, etc.) turn off when I turn my headlights on. Talked to an AutoZone guy and he mentioned that it may be a short in the headlight or dimmer switches. Have a headlight switch on order for $15. I can change it myself, if that's what the problem ends up being.

Does the Check Engine light go off when the headlights are turned on, or just the O/D Off, 4WD Low/High and Cruise control indicators? These are the only lights controlled via the headlight switch, the check engine light is not. If it's all of the instrumentation lights that stop when the headlights are on, including the turn signal idicators, I'd suspect more a grounding issue for the instrument cluster.

All of the interior lights are fed from the same lead off the dimmer module, radio, ashtray, window/lock switches, instrument cluster backlighting, etc.

-Rod

Thanks for the reply. Sorry for not being more specific.

The only lights that I've seen go off when the headlights are turned on are the cruise control and the O/D off. My engine light isn't on--save for when I initially start the vehicle, and that even illuminates when I start the engine with headlights on. I haven't checked if the 4WD High/Low illuminates or not because I haven't been anywhere that requires engaging 4WD yet. I just noticed that the cruise control and the O/D off lights did not illuminate until I drove a little bit with my headlights off yesterday evening.

My radio works fine, so do the power locks, doors, windows, and interior lights. I don't think I have any lights for the HVAC control area.

With that new info, it sounds like there's a good chance the new headlight switch will fix the problem.

-Rod

No dice on the switch. Stuck a brand new one in there and have the same problems. Could it be the harness that connects to the switch? A wire, maybe?

Time to get out the test light or voltmeter. You need to verify that there is voltage leaving the switch for the dummy lights in the dash (terminal 8 at the headlight switch, orange/black wire) and the instrument illumination (red black wire from pin 7 of the dimmer module). Trace the voltages all the way from the switches to the instrument cluster. If you don't have voltage of from the switch, verify that you have voltage to the switch from the dimmer module. However, you said the dimmer works for the other interior lights....

You could also check the dimmer relay within the relay module to make sure it's working properly. From the quick look though, it appears the dimmer relay would not be part of the circuit when the headlights are on though.

-Rod

I'll get on that when I have more time to tear apart the dashboard. Maybe this weekend. I have a multimeter that I've been itching to use for a while.

There is one thing I've noticed. When the headlamp switch is in the OFF position, there is a green light illuminating the the OFF, DRIVING LIGHTS, and HEADLAMP icons. When I turn the switch to turn on the driving lights or headlamps, the green light shuts off. Does that help narrow anything down?

That certainly sounds like a ground issue. It sounds like something is getting its ground through the bulbs causing them to illuminate.

-Rod