My 2004 F-150 is losing it's mind and in turn I'm losing mine. The rear brake lights and license plate lamps are dim when the park/headlights are on, when you apply the brakes the lights get just slightly brighter(third brake light works fine).And...the turn signals work fine until you turn the park/headlights on and then they flash fast along with the license plate lamps? And with the lights on the signal lights will stop flashing if you apply the brake. This has come and gone three different times now, at different temps and times with no rhyme or reason. By the way it is a supercrew 4x4 with factory towing.Please help........THANKS!

 

I don't have access to the '04 schematics, but it sounds like you lost a ground connection in the wiring somewhere around the rear end. The parking lights are grounding through the turn/brake filament, and then when you hit the brakes or turn signal, the power has noplace to go when the parking lights are on, and the light goes out. You see it commonly on boat trailers with the same problem.

Without seeing the schematics I can't say it conclusively though.... If anyone can post one, I'd be happy to pour over it until the answer comes to me.

 

i will second the poor ground. easiest way to check without using the ohm meter, as this throws some without electrical experience off, is just put it on the volts scale and check the voltage. pop a bulb out and probe the contact. if thats around 10 to 13 volts it has to be the ground. i have always found dim head lights to be the ground. for what ever reason they do a good job on the power side but not so on the ground.

 

THANKS-THANKS-THANKS---let me try that and see if it works...paul

 

checked the voltage at the tail/turn signal light and got approximatley 11 volts----is this consistant with a goofy ground? and would the reverse lights going out first give me any direction to start or is that just another indicator? THANKS AGAIN!!!

 

It was a goofy ground-couldn't find the origin, so went around the problem. Ran an additional ground to the incoming left tail/turn wiring harness and TA DAH! it worked.

Thank you for your concern and posts I appreciate it!!!


HAPPY THANKSGIVING!!!

 

Happy to help! Glad it's working again.

Often times, the bad ground you have can be caused by a connector not fully seated, or sometimes a single pin will push itself back out. It's rare, but happens every so often.

Make sure you don't have any exposed copper at your connections, otherwise you'll have this same problem again after a few rain storms.

-Joe

 

Don't know if you want to try to locate the bad ground or not.

Left Rear Tail lamp ( along with righ rear, license plate lamps ) are via a splice S401, and then via 3 more connectors and one or 2 splices depending on if it is a SuperCab or SuperCrew. then to a single ground G303.

G303 is also for :
Reversing lamps
The S/T/T lamps ( you know that one ).
Keypad switch on driver's door
door lock switch driver's side
exterior rear view mirrors
Door ajar switch driver's side
The BSM
- Super Cab / Super Crew in addition to above
roof opening panel switch
DVD player
interior / map lamps
power rear slider
seat adjust switch ( power seats )
heated seat module driver's side

By the list, and without notoation that these other items were not working, starting with Splice S401 and Conenctor C405 is the first place.

S401 This is in the harness that runs in the rear cross member. Look under the rear of the truck, follow the license plate wiring up to the wire loom that contains this splice ( same side to side harness ).

C405 is in the rear of the truck, about the same location along the frame rail as the trailer tow connector adapter. might have tot drop the spare to get a good look at it. This is the driver's side frame rail
This is a picture for the Trailer tow connector ( circled in red ) but per 151-22, this is where it shows the Conenctor C405 :

C405 is a round black connector. pin #6 is the black wire for the ground circuit #57. I could not get a good look at it, but I think it is the round one shown in the diagram above, it is on top of the frame.

Good luck

 

appreciate the additional help! Everything is fine right now--keeping my fingers crossed!! thanks,paul