I have a 2007 F250, Powerstroke 6.0 diesel. The rear tail lights are from a 1994-1999 Cadillac Deville. The other day my signals stopped working. They only work if the brake pedal is pushed. This goes for the flashers as well. Any body have any suggestions where to start.

 

Your taillights are from a Cadillac Deville?

 

It looks sharp, but this is how I bought the truck. I didn't do this modification. I just wanted to know where I should start to trouble shoot this issue. Like the turn signal switch, the brake switch(at the pedal) ect.

 

The truck is trying to tell you to change them out for some OEM ones. GM parts do not go on Ford trucks, period.

 

You may want to check the grounds, usually(but not always) when funny things happen with lights, it's the ground.

 

Well I figured it out. The 20 amp fuse to the trailer wiring and a blown tail light
The handy multi meter saved the day. Always test the fuses.