Ok so first off I have a 2006 f150 HD.


so the other day I am driving down the highway and someone waves me down and tells me my brake lights arnt on. So when I get home I check and notice that the lights are on but seem to be pulsating. everything else works normal, headlights, brake lights, reverse lights, turn signals, everything works except that rear running lights. This started happening after I heard news from the local mechanic that I needed a new battery.


so the next day at work on the way home same thing, but this time the rear running lights are out completely and also while driving my cluster and dash lights flashed on and off a few times.


I had the alternator checked and it was good, and also had the battery replaced at this point. but after everything was said and done, the same problem happens. no rear running lights but everything else is good. I check the fuses and everything seems to look good.


also on a side note I noticed that when I have my auto light function on I have the same problems as above and also my dash lights wont come on in the auto function, but do come on when the lights are turned on manually.


I have no idea what to do next. The only thing I can think of is maybe the light switch itself is bad and making them not work? any help I would greatly appreciate because no one seems to have an answer.

 

Have you checked fuses to make sure they are good? It may be hanging on by a thread to make the panel and parking lights not work. I think it may be fuse 6?

 

Did you replace the battery yourself? I ask cause if you didn't check the ground..could be just loose enough to cause it. just for giggles id check the light assemblies in the rear for possible loose bulbs wires etc...just to check that off the list.

 

Check the fuse for the keep alive power to the instrument panel. It's fuse 21. I was messing with the interior lights and accidentally popped that fuse. Cut the interior lights, radio, and instrument cluster that I noticed.

 

Fuse 6 is the parking lights, BSM, and instrument panel illumination.

 

yea I checked that fuse and it looks good and I check that relay as well and it seems fine, I might order a new one just to see if it works.

as far as the battery I was having this problem with the old one and the new one. I had a local auto shop install and test the alternator. Also they checked fuses and rear taillight wiring and didn't notice anything.

also an update. so today I was trying different combos and noticed that when my headlight switch is to the on position, everything works except my rear parking lights. Now when I put the light switch to auto, my headlights and rear parking lights work, but my dash lights don't work, front parking lights don't work and my fog lights don't work. WTF? I have no clue what is going on.

for some reason I think the culprit is the light switch itself, maybe the low battery volts fried it out? all lights work but in different combos.

 

WTF is right. I think you are on the right track with the switch though. I'm not sure if there is a way to bypass it and Test it out or not.

 

Here are the wiring diagrams which may help you track it down...

 

ok so I got the new headlight switch in and same exact problem...... wtf

 

I would try checking the ground(s) like another user suggested, as well as the battery connections. What exactly do you mean by the lights were pulsating? That would indicate an issue with the alternator rectifier bridge (I believe that is the component I am thinking of).

This is a long shot, but you might try it to cross it off as a possibility. The photo cell located either on the top of the dash or in the rear view mirror that actuates the auto headlights may be able to be disconnected. I am not 100%, but I think it may be the black dome on the top of the drivers side dash that has a red LED that flashes with the ignition off. Anyone else know if this might be the photo cell?

Like I said, a long shot, but it might be something.