I recently purchased a used 2003 F250 Crew Cab with the V10 engine in it and I have been chasing an electrical problem that is really starting to get under my skin.

For no reason I can find, while the truck is parked, turned off and no one has touched it, the brake lights will simply turn on (along with the after market electric trailer brake controller) as if someone has stepped on the pedal. This includes the upper third brake light. Pulling up on the pedal does not help.

The first thing I did was remove the brake controller but this had no effect. Next, I replaced the brake light switch. This appeared to fix the problem, but then my cruise control would no longer work. I purchased another switch from a different parts store and then all seemed well for about a month.

This evening, my neighbor knocked on the door to tell me my lights were going on and off by themselves. He said he had been watching and they were staying on for as much as 3 minutes before going off again. This cycle was continueing when I came out to check it.

It is late and I just wanted to stop them from coming on, so I checked the owners manual and I removed both the #18 and #24 fuses (Turn Lamps/Brake on-off switch [high] & brake pressure switch) but the brake lights continue to cycle on and off. This is despite the fact that I last drove the truck two days ago!

I used to own nothing but Ford trucks, but my last two trucks were lemons and I switched to Dodge. After having my Dodge for 8 years, I decided to give Ford another try. So far, I am NOT impressed. The trucks are great. The electricals suck (My overhead cluster doesn't work either, I understand this is a common problem)

Can anyone help me figure out what to look for and tell me how to fix this? I am no electrician and I can promise you that no shop will be able to replicate the problem if my luck holds the way it normally does. I have no idea what to try next. All I can do right now is disconnect the battery.

On the plus side, my Ford does pull my camper a lot easier than my Dodge did.

 

Check for an aftermarket alarm or remote starter or any other modifications to the circuitry.

When that truck left the factory, the brake lamps could only be turned on via the brake pedal switch fed by fuse F18. Removing F18 SHOULD have disabled any source of power for the brake lamps. Since it didn't there has to be a non-factory source of power getting to that circuit.

 

[quote=projectSHO89;11819601]Check for an aftermarket alarm or remote starter or any other modifications to the circuitry.


X2, aftermarket something in there somewhere......... Listen for a relay clicking that is timed to the lights flashing.

 

look for corrosion at the trailer plug-in. that will backfeed all kinds of stuff... i have to replace mine almost every spring with the road salt here in MI.

 

The trailer lights, unless hacked up by a previous owner, are isolated from the primary circuits by relays.

 

Thanks guys.

There is nothing on the truck anywhere that would suggest to me that any kind of alarm system was installed at any time. I DO hear a relay clicking somewhere near the drivers side dash area when the brake lights come on and off. I should note though, that I also hear a relay clicking in and out when nothing happens (and the truck is off, keys are out)

All wires appear to be factory and untampered with. Even the brake controller is plugged into a factory harness. My truck is equipped with both a 4 pin flat and a 7 pin round connectors. I use both depending on the trailer I am pulling and both appear to be clean and in good condition and both work perfectly. (This happens when no trailer is connected)

When it happens, both brake lights + the third brake light + the brake controller all light up. The brake controller shows two red bars No other lights come on. Also, I have never
noticed this problem while the truck is running and it normally seems to happen after the truck has been sitting for a day or two (at least, thats when I have noticed it).

Is it possible that something in the computer could cause it? Since I pulled the only two fuses I could find that appeared to have anything to do with the brake lights and they still stayed lit, I assume I either didn't find the right fuse, or power is being fed from somewhere else? Again, I am no electrician.

Also, this may offer a clue and is something that I forgot to mention before.

When I replaced the brake switch the first time, I noted that there was a piece of non-factory electrical tape on the wires leading to the switch. Also, the plastic plug has a "cover" part to it that snaps down over the wires and this was undone. The electrical tape did not appear to be doing anything as it was loose and barely hanging on and the wires all appeared to be fine. I removed the tape, snapped the cover back down, and installed the new brake light switch. And except for the cruise not working, all was well. When I replaced the switch the 2nd time, all looked normal, and for the past month or so, all has worked normally.

I think I will go back in and take another close look at those wires to see if they really are OK. Any hints on what to look for besides the obvious bare wire? I assume at least one of these wires is hot at all times? If so, I will start with that one.

 

Find the click, aftermarket part is most likely still in there.

 

The computer has nothing to do with the brake lamp circuit, so there's no worry there.

Additional question: Are any other lights (interior, etc) also affected?

 

No other lights are affected.

Neighbor reported that it was doing it again last night about midnight. I'm trying to catch it doing it again so I can find where the clicking is coming from. Problem is, it's not constant. More like "flare ups"