I have owned my 2003 F150 supercrew for a couple years now and bought it with a topper attached. I pulled the topper off and sold it just to realize the 3rd break light on the truck had been disconnected. I have looked all over the truck to find where the previous owner may have disconnected the 3rd break light to no avail. Can someone please give me some suggestions on where to look for the disconnect point. I checked the bulbs and they are fine. Pulled the 3rd tail light unit off and checked the wires and they are all connected. I pulled the cab light off so see if I could see a connection between that and the tail light and couldn't see the harness. Would I need to pull down the head liner to access the harness? Does the third break like run through the cab or is there an access point under the cab? I'm really at a loss here and have been pulled over a few times for it being out.. So any help here would be very much appreciated!

 

The third brake light wire usually feeds through the interior dome light. I would check fuses first however. I can't imagine disconnecting the wire but anything is possible. You can also check the passengers footwell kick plate as the POC. If you have access to a wire diagram it will help you locate the source of power. Good Luck

 

Yeah, a wiring diagram would be a huge help in this situation but unfortunately I don't have one and haven't been able to find one that has been of any help. I will check the fuses, but the dome light in the truck works, and from what I have seen the dome light and the 3rd break light are on one circuit so I am not to hopeful it will be a simple as the replacing a fuse, but i will try that non the less if I am able to find what fuse is the problem. What color would the wire be coming from the passenger side kick plate? I will also look there. Thank you!

 

Sorry I wasn't very clear. The wire for the third brake light would only pass through the dome light, not connect there. I would try first unplugging the light assembly and power it with another source like a 12 volt battery tester or small jumpers from the battery to confirm it's working. Second I would get a 12 volt test light and probe the plug whit the brake applied to confirm or eliminate the issue is at the lights location. Often a bad ground can cause your issue. I googled a lighting wire diagram for your truck and there are a few images that may get you to where you want to be. As far as the wire color goes, what ever the power side of the cab plug is, it will be the same any where else in the system. Good luck

 

In my '01 Screw, the 3rd brake light wiring goes from the light, across the top of the back glass to the passenger side, then down the rear corner of the passenger side (under all the trim, of course), into the passenger side sill channel at the bottom of the doors, then runs up under the dash on the passenger side.
That's as far as I've traced mine, so where it goes from there, I have no clue. However, water is known to get trapped in that channel and corrodes the wiring/splices. May check that out just by prying up the sill trims and unwrapping/inspecting wiring. My interior lights were all jacked up because of a corroded splice right at the bottom of the door pillar where the front passenger seatbelt is attached.
Hopefully this helps some.