Hello! I have a very limited knowledge on the electronic workings of vehicles and have run into a problem.


Essentially the backlights to the dash are not working and possibly unrelated the brake lights don't illuminate when the headlights are on and the brake pedal is not depressed.


Here's what I can tell you about the dashboard lights:


The panel dimmer control has no effect on waking up the dashboard lights but is still functional because the interior cabin lights will come on when the control is moved past the upper detent. I could not feel a lower detent. Warning lights and odometer still work. Air con/radio backlights DID NOT work either. This was all with headlights in ON or AUTO position.


Last night my girlfriend and I were driving somewhere, she was in her own car behind me. She said that the brake lights were completely dark unless I was braking. I'm not sure what to call it when the brake lights stay on while the headlights are on but whatever it is my truck wasn't doing that. The brake lights would come on when the parking brake was engaged, when the truck was in park, or when the brake pedal was depressed. Reverse lights and turn indicators worked.



I've done quick internet searches and couldn't really find anything. I haven't installed a new radio or done anything. There is a trailer brake system installed but it hasn't been a problem since no trailer has been connected in a while.



Are these problems related? Can I make a quick fix?
Thanks so much!

 

UPDATE: Checked a bunch of fuses, the location 17, Exterior Lamps fuse was blown. That was the only one I could see that was blown (I don't have a voltage tester). Will try to get another one to see if the problem is fixed.

 

UPDATE 2: Replacing location 17 fuse did nothing. In fact, now the brake lights aren't on when the vehicle is in park or when the parking brake is on, the light only comes on when the brake pedal is depressed.

 

The lights you are referring to are taillights. They should be on when the headlights are on (i.e. at night). They are dim compared to brake lights. the bulb has two filaments, bright and dim. the circuits feeding the bright and dim filaments are not related. It's not a case of "suddenly it gets more power" when the brake lights are on. That is an unrelated circuit.

 

P.S. The problems might be related if they're on the same fuse. Get the owner's manual out and look up the fuses, and look up the taillamp fuse.

 

http://www.fordservicecontent.com/Fo.../04f23og3e.pdf

Not finding it. Which do you suggest it is?

List starts on 194

 

Well, I was afraid of that. They seem to move around unpredictably from truck to truck. I can't do any better than 17, "exterior lamps" but I admit I don't trust the manual completely.


Do the front marker lights work at all? If they do, then I guess the fuse for the back ones is good.


Whether or not they do, if you are convinced the fuse is okay, I think the step after that would be probing wires at the light switch. The light switch could conceivably be the problem itself.

 

Pardon my lack of knowledge of identification terms but are the marker lights the turn signals? Or are they orange lights that run constantly like the rear ones are supposed to? I can troubleshoot when I get home today.

I realized that I didn't check the box under the hood, I only checked the auxillary fuse box under the steering column. I'll report back with findings once I'm able to.

 

Did you check the bulbs to see if the tail lamp filament is burned out?

 

Marker lights = tail lights = running lights = parking lights.

----OR----

Brake lights = stop lights.


Two different functions, different fuses, different switches. The only thing those two circuits have in common electrically are the ground circuits inside the dual-filament bulbs. FWIW, the instrument illumination circuit is wired to the running light circuit.

It is essential that you correctly identify WHICH function is being discussed so that you get the correct information.

 

I'll try to check that. Seems weird that both would go out at the same time though?

Thank you for clarification. I'm doing the best I can to identify the function by explaining the situation.

Am I correct then in saying that the front running lights are working? When I turn the switch on the "headlights" work as they should. The rear running lights do not work. The brake lights do work.

 

for Dually

All of those do run off of fuse 17. Id be checking for voltage at the headlight switch.

If you are not educated in the ways of circuitry, this can be overwhelming. At least, here are a few pics of the exterior lighting wiring diagrams.

A freebie source for more, go to autozone.com, register for MyZone, add your vehicle, repair guides, wiring diagrams, select system.

Hope this helps.

 

At the switch, a 10 gauge wire(thicker) that is tan with a white stripe is the 12v feed from fuse 17.

A 14ga wire that is brown at the headlight switch is the output 12v when the headlight switch is in park or on(Forget about the auto lamp bs for now)

If you have the means, check those now and report back.

To test the brown wire, you need to have the switch hooked up, set to on or park, and either pierce the wire jacket to test for 12v, or probe the connector where the wire enters the connector (This is a better option, as to not make pin holes, but often cannot get a probe in there.)

 

This set of cartoons shows the instrument panel lighting. First pic shows fuse 17 to headlight switch, then on to B(in triangle) to next pic B(in triangle) to lights.




This shows that 2 different systems get their 12v from the same brown wire at the switch. Since neither the panel lights or the tailights(external lighting) work, this tells me the switch is bad, provided that you indeed have 12 volts on the tan/white 10ga wire at the switch.

Clear as mud??

 

if so, pick yer poison

Headlight Switch at AutoZone.com - Best Headlight Switch Products for Cars, Trucks & SUVS

http://www.ebay.com/sch/i.html?_odkw...+f250&_sacat=0

Good luck.

I don't work for or represent AZ. Just an easy reference source for diagrams.