Hi sorry to start a new thread but i am at a dead end 97 f150 new style 4x4 i was installing third brake light in shell and shorted it (long story my bad) i found the fuse that runs the turn and park lights to the trailer plug but the brake lights dont work and my third brake light on the truck stopped working all other lights on the truck work fine i have tested all fuses and relays w/test light and ohm meter that i can find, three fuse boxes under hood one under dash checked as much wire as i can find i can only think i am missing a fuse somewhere by the way it blew thanks for any ideas
John
SLC Utah

 

Not too sure what a 97 f150 new style 4x4 is, what do you mean by this ?

The Truck's CHMSL does not work ?
did you check the cab fuse panel fuse #13 with a meter on both sides to a known good ground ?
- not too sure why you are testing the fuse for the radio, or how you are doing in with the test light.
- This fuse is hot at all times, so both sides of it should be hot regardless of what you are doing.

If this fuse is good on both sides, that means you should be able to get the truck out of gear after starting it.

If so, check the CHMSL bulb connector for power at the socket when the brakes are one.

 

Hi thanks for your reply what's a chml i tested all fuses with a simple ground to power test light as well as any wiring i could access and i pulled and tested all of the relays i could find with a ohm meter the relays have the internal wiring diagram printed on the side of them so you can tell what prongs to run your ohm meter through i dont have a problem getting the truck out of gear the rear lower brake lights on the truck work fine its just the third light on the truck and the brake lights for the trailer at the truck side 7 pin female sockett

 

CHMSL = Center High Mount Stop Lamp

check the CHMSL bulb connector for power at the socket when the brakes are on, what is the result ?

The 7 pin trailer tow adapter, you said the turn signals work, this is the same circuit for the stop lamp.
When you step on the brakes, the left stop / turn is dead ?

Are you using a meter or test light on the 7 pin trailer tow adapter or a trailer to test with ?

Not too sure how the trailer tow adapter turn signals can work, and the truck's stop / turn signals work correctly.
They are the same circuit pat for stop & turn.
The Output of the MFS to the truck's stop / turn lamp is the power to the trailer tow adapter stop / turn relays ( L & R ).

 

Thank you again for your reply i cant figure out how the stop, park and turn lights to the truck work just fine and the turn and park work fine to the seven pin but the brake to the seven pin does not. BTW i pulled the shell so i could get to the cab over head 3rd brake light (CHMSL) the bulb was blown along with the 2 reverse bulbs in the same socket replaced brake bulb on the truck now works fine although all 3 socket's were lets say a little melty. BTW on the seven pin at the bumper when you hold the brakes the left and right pins stay steady on until you hit one of the turn signals then that one blinks the other still shows brake just not through to the trailer there is one pin that does nothing. now remember all of this has worked for the last 5 years until i shorted my third brake light for the shell to the shell
Thanks Again for your reply's SSCULLY
John
SLC Utah

 

You tested the 7 pin trailer tow adapter on the truck and they work correctly ?

Are you testing with a meter ?
If so, does it show the correct voltage ?
What are you using for a ground ?

What pin does nothing ?

Where did you hook up the CHMSL for the Cap when you shorted it to ground ?