hello, I have a 1990 aerostar 4.0 eddie bauer. I cant figure it out but when I turn the head lights on the dash lights go out. with the head lights turned off, the dash lights work just fine. Anybody out there experience this problem? I have changed the headlight switch, and the panel dimmer switch.

 

johnzmur,

If you've changed the headlight switch and the panel dimmer switch, you might try the high/low beam switch...although I don't really think this would cause this problem...usually this problem is associated to the combination headlight switch/instrument panel dimmer control...which you say you've replaced.

Try doing a search on this forum for headlights, instrument panel lights, dimmer, etc. LOL

Ron

 

Just a wild guess, but maybe this is somehow grounding thru the parking light circuit. Have you checked the ground connection under the dash?

 

John,

I thought about this a lot and it still seems to me that your problem has to be directly related to the headlight/instrument cluster switch. Check the switch while you have it removed from the mounting in the dash and see if you have the same problem.

Just so we're on the same page, when you pull the light switch out to the first detent, you have dash lights, running lights, and the instrument cluster dimmer works fine. Then, when you pull the light switch out to the second detent, you have headlights and running lights, but loose the dash lights. Is this correct?

Ron

 

hello again and thanks to all that replied

This one is a rocker switch not a push pull. and yes all of my lights work fine except the dash lights when switch is turned on. turn off the head light switch and they work fine. I noticed that the floor shift light quit altogether at the same time. I wonder if the problem could be in there.

 

Trying to get a better understanding of the problem here. You have the digital dash that lights up. The headlight switch is the rocker type switch. Can you verify what happens at the different switch settings.

Switch ------ dash ------ tail/side marker -------- headlights
off ----------- ON ------------ OFF -------------- Off
park ---------- ?? ------------- ON --------------- Off
on ----------- OFF ------------ ON --------------- On

Under normal operation when you put the switch in either park or on, the dash lights become dimmer. Just how dim is based on the position of the dimmer control. You said you replaced both switch and dimmer.

I need to look at the wiring diagram (not with me) to have a better idea but, it would help so know if the dash lights go out when the switch is in the park position.

 

well tom,
there is no park position, there is just on and off. I sure appreciate every body's help, hope I can figure this out, as my wife doesent want to drive it at night with no dash lights and i cannot afford a mechanicto chase the problem.

oh yeah. I should mention that the head light switch and the panel dimmer switch are seperate. the panel dimmer is under the dash by your left knee

 

dear tom,
I forgot to tell you, The chart that you built reflects excactly with what is happening, ony there is no park position

 

John,

Are you sure there is no park position?

I have a 1990 XLT, and the rocker switch is definitely 3 position: OFF, PARK, and headlights on. Your symptoms suggests something wrong with the rocker switch, such as a bad contact feeding power to the instrument lights (this includes the lights for the overhead trip computer and the shifter indicator on the floor). I'll have to look at my wiring diagrams to see how the switch is configured before I can figure out any more.

 

John,

Are you sure the headlight switch you replaced was the correct one. From Tom's posts it sounds like you should have a three position switch instead of just an on-off two position switch. It may be that the two position switch is wired to pass power to the dash in the off position, but not in the on position. I would check the switch to be sure it is the correct one.

If it is the correct switch, then I was wondering how you turned off the dash lights during the day; but, I realized that if you have the digital dash as Tom indicates, then I assume they should be on all the time when the key is in the start or run position. In that case, what is the relationship between the two systems (headlight and dash light)? I would think none, they should be two separate systems. How then would turning on the headlight switch cause the dash lights to go off? Only if the headlight system is drawing all the available power. Possibly a bad alternator/voltage regulator? or an electrical problem in the headlight wiring?

Just thinking out loud.

Ron

 

I too am suprised that there is no park position on the toggle switch. I had a 91 that had that switch and the dimmer was a dial down at the bottom of the dash. It took me a while to find that as I didn't have an owner's manual.

I'm sure it had a park position. I've never seen a car that didn't have one. How else would you turn on the exterior lighting without the headlights?

I still haven't looked at the diagram yet. Take a look at the switch and the one you took out and make sure about the park position and let us know what you find.

 

sorry fella's you are right there is a park position, but when you put the lights on park the dash lights go out

 

So the problem sounds like wiring or the dimmer. With the park and head lights off, the instrument panel gets the full illumination as long as the key is on. When you turn the headlight switch to either the park or on pisitions, it will change the circuit powering the instrument panel lighting to go through the dimmer. Either the switch itself is bad, the dimmer is bad, or the wire that goes from the light switch to the dimmer is bad. (I assume you've already tried turning the dimmer to either limits.)

One failure I saw in the dimmer in my van was when I did not have it at the full brightness position. It was nearly there, and this position generated enough heat to blow its thermal fuse. It can happen to a new dimmer. I ended up bypassing the fuse, and making sure that if I ever used the dimmer again, I dimmed it a lot, or none at all.

 

John,

A quick check for the dimmer switch (rheostat) would be to disconnect the wiring and using a multi-meter check for voltage coming into the switch. It should have only two wires connected to the dimmer switch; one for power in, the other for power to the dash (power out). If you have no power to either pin with the headlight switch in the park or on position, then your problem is before the dimmer control and you will have to check the wiring from the headlight switch to the dimmer contol. If xlt4wd90 is correct and the dash is powered by a separate circuit with the headlight switch to off, you could have a broken wire from the headlight switch to the dimmer causing the problem.

If you have good power coming to the dimmer with the headlight switch in park or on, then check the dimmer control for continuity. Although you have already replaced one dimmer control, I'd check the dimmer control's resistance with the multi-meter while turing the control wheel. If you still have it, check the dimmer control you removed also.

If you get a reading that decreases the resistance while turning the control wheel, then your dimmer control is good. If you get no reading, then the dimmer control is bad or the internal thermal fuse had been blown. In either case, we need to determine what caused this failure. I guess you could have gotten a bad replacement dimmer control, but I'd lean more towards there being another problem that caused the original dimmer to go bad. You could have a short in the wiring going from the dimmer control to the dash panel causing the dimmer control thermal fuse to blow.

If the dimmer control checks good, then you have a problem with the wiring from the dimmer control to the dash. I would not rule out a short to ground. It could be bad enough that it does not allow enough power to the dash for the lights to work, but not a bad enough short to blow the fuse or thermal fuse. Or you could have a broken wire that opens the circuit.

Of course, you could try using a jumper across the two connectors to see if you get your dash lights back (effectively removes the dimmer control from the electrical circuit), but you run the risk of blowing a fuse at the least and harming the dash illumination system at the worst.

LOL

Ron

 

Not to sound like everyone else but.....Are you sure that the dimmer(big honking rheostat) you installed was good?I had the same problem in my 90 Eddie Bauer and that was the cause.
I believe there is also a small relay located under the dash by the steering column that I had checked also when I had this problem.Can't remember what its called,though.I know I have it bookmarked in my manual so I will check it and see.
just my two cents.