I have an 06 F150 5.4l XLT with the factory 7pin and flat 4 trailer connections. About 2months ago I had my blinker start going about twice as fast as normal when applying the brakes. I changed out the pass tail light and all was well. I recently went camping down a very long and very bumpy dirt road and the problem came back on my way home. This time I checked fuses and bulbs and then finally tried messing with the wiring harness for the trailer/tail lights thinking they might have jarred loose. After squeezing the harness's together my blinkers started working normally again (this may have been a fluke). Needless to say they are on the fritz again. So..

-Blinkers work fine as long as the running lights or brakes are not on.
-If the headlights and brakes are on, blinker does not work at all.
-With the running lights off and the brakes engaged the blinker goes twice as fast and all brake/tail lights are dim and flashing.
-I believe the brake lights go out altogether when the running lights and blinker are going at the same time.
-hazard lights work perfect no matter what.
-I have noticed a clicking in the fuse box when engaging the brake or switching on the running lights (just one click when engaged and one click disengaged). When everything works fine I do not hear this click.
-I disconnected the brake switch on the pedal and tried the blinker with running lights only. Still blinks fast.
-I changed out most of the exterior bulbs (headlamps and cargo bulbs have not been changed).
-When I plug in my boat trailer lights, things mostly return to normal. With the running lights and brake engaged the blinker runs just barely faster than normal. Other than that lights are fine.

Sorry this is so long. I just wanted to give you guys most of the info I have to this point. Thanks for any ideas you might have.

 

Have you tried changing the tilt wheel all the way up or all the way down ?

Might sound like a dumb idea, but remove the trailer tow adapter from the factory wiring, to see it is a problem back there ( since you posted you had pushed something together back there ).

You will want to drop the spare , to get to it easier. There is a large connector.



This will remove the 4 & 7 pin adapters from the mix.

Also a question on this :
Not sure what you mean by this. Is this the turn signal does not blink on and off ( i.e. there seems to be a bleed voltage that keeps the high wattage element partially lit ) ?

Could be a few places, but the major locations
1. MFS or the connector for it
2. Trailer tow adapter
3. tail lamp housing area ( back ground ? )

 

Sounds like you have a dead short someplace making the system thing that the blinker is out and causing the fast blinking. Could be in the wiring but if you are hearing a pop from the fuse box my guess is that it is a bad relay. The fuses could still be fine and the relay has gone bad or maybe has just come a little loose?

 

Wow, thanks for the replys so quickly. I have already disconnected that harness and the blinkers still run fast. I wasn't sure if that meant anything or if its normal because the tail lights are unplugged. I also turned the blinker on a wiggled all those wires back there hoping to get a reaction, again nothing.
The voltage at the tail light sockets are ~12volts when the blinker works normally. When the running lights are on and the blinker is running fast the voltage was ~6volts. I checked the fuses per my owners manual that had anything to do with lighting. They are all ok.
I have tried moving the steering wheel up and down and even pulled the covers to get to the MFS. I didn't dig in to that thing but it looks ok as far as connections go.
I will get back to you guys on what the brake light does when the turn signal is on. I believe all 3 brake lights flash faintly with the fast blinking. I also believe they are all dim. If I remember right, the front marker lights and signals are normal brightness but they also flash quickly. I will double check when I get home tonight to make sure. I think Im going to pick up the actual flasher relay that you can hear in the dash and swap that out. Seems like the easiest thing. Thanks again.

 

I tried unplugging the relays one by one and pressing on the brake. I couldn't eliminate the click. Is it possible for a fuse to click like that? I tried pressing all the fuses and relays in as well just to make sure.

 

A fuse shouldn't click. If it did only once and it would be blown. I still think it sounds like a bad relay so maybe it is the flasher in the dash? Good luck!

 

Sure the click you are hearing is the Brake Pedal Position Switch / Shift interlock.

My '06 has a click click at the top of the pedal travel.

With the voltage problem, best to check the sockets on both sides, to make sure there is a ground. Check the bulbs installed also, to make sure none of the pins are twisted around.

If the voltage drop is 50%, I would take a SWAG that you are finding ground through another item, thus the reason for the voltage drop.

 

There is a click I can hear at the pedal which I assume is the brake light switch. There is also a click around (sounds like in) the fuse box that follows the click from the brake light switch. Happens right at the top of the pedal.
Also, my initial post is incorrect. My lights do not work properly at all when this issue shows itself. I thought the blinkers work fine on their own but that is not the case. They blink at normal speed but so does everything else.
I tried a new MFS and turn signal relay (the one under drivers dash) as well. Neither fixed the problem.
Im starting to suspect the alarm system because remote start does not work now unless the key is in the ignition, doesn't even have to be in the "on" position.
I will have another look at grounds though. I found the one for all the rear lights in the cross member behind the spare. It looks fine. Thanks again for the info.

 

Does anyone know if there is a list or diagram of wiring ground locations I could work through with a meter? Im running out of options here and im hesitant to take it to the dealership. Lord knows how many shop hrs I would be charged for to figure this out.

 

to make a long story short. i had the same problem with my turn signals. and i had the l.e.d light bar pluged in. all the water finally ate away and rotted the wires causing to to short out and make my lights act weird. i disconnected the bar and all went back to normal.

 

So, where was the L.E.D light bar at? I have not installed any L.E.Ds on my truck. Was it part of the factory wiring that shorted?

 

I realized my cruise control does not work either when the lights are acting up. I also had everything start working normally again after sitting in the driveway for a few days. I drove it around until it failed again so I could put in the new MFS. That didn't fix it. Any ideas on what could affect the cruise control?

 

well it was the tailgate light bar/turn signals. and it was puged into the rear hitch where i guess the trailer wire harness would go.

 

i never used the cruise control when i had that problem.all i noticed was that the brake lights would stay lit with or without pressing the break, and the blinker would stay on steady. it was reali screwed up. before i too it to the dealer i unpluged my light bar and it was all good. it even screwed up my remote start..

 

Starting to sound like the brake switch ( which is also the shift interlock switch, but that is a different circuit ).

Does the 3rd brake light work correctly ? Usually when the CC has an issue, there are LED bulbs in the CHMSL position without a resistor.

Might want to pull it, and see if the CHMSL bulb is OK ( no corrosion problems ).

That is a swag, but the CHMSL is directly wired to the brake switch ( does not run through the MFS ).