I guess I have the dreaded 3rd brake light leak. I've actually been seeing some water at the bottom of the vinyl piece under the rear window every once in awhile. I have the base model with the rubber floor mat so its easy to spot it when it leaks. I was washing it the other day and I noticed water was getting under the rear lower edge of the light lens. So, I just ordered one of the new lenses with the improved gasket (7L3Z 13A613-B). I'll install it and see what happens. If it doesn't stop, I'll know its the rear glass seal. I'm pretty sure it's the lens gasket so I don't look at this as a shot in the dark. Water doesn't appear to have been getting into the lower cab corners - there's no rust or blistering. I guess I could drill a small hole in each side to see if there's any water and put a screw/rubber washer back.

 

Okay, got my part and the new seal is a lot thicker than the original. But I didn't install it. When I got the old one off, I could see that the wiring harness had no connections in it and disappeared under the sub-roof. The new part has a pigtail with a connector, so there is no way to hook it up. So, I cleaned up the gasket on the old one which had a lot of trash under it along with the sealing surface of the roof, gave it a thin bead of clear RTV silicone and put it back in place. I could see from the marks on the sub-roof that it definitely had been leaking. End Part One.
Part Two: Painful Realization
Shortly after finishing the job, it hit me; all I had to do was disconnect the pigtail from the three lamps and throw it away, then connect the three wires from the harness to the three lamps - same connectors all around.
So, I'm keeping the new part to install at a later date. Rain is expected Thursday so I'll see if my fix worked. You have to be careful what you use for this purpose. You probably will have to take it back off at some point to replace a lamp, so you can't use a solvent glue - that might attack the paint too. Just regular RTV silicone rubber is probably the best you can do.
On both the old and new units, the seal is permanently attached to the lens. If you decide to do what I did, make sure everything is clean, then run a 1/8" bead around the seal like any other gasket. The screw holes in the lens have a rubber seal in them but it comes apart, so I put the clear RTV in them too before the screws.
I don't know about water from this leak getting down into the cab corners, so I decided instead of drilling holes to find out, at some point I will pull off the vinyl interior parts and roll back the rubber mat so I can see if the water can get past the cab floor down into the corners. Might be able to just roll back the mat and see without taking anything apart. I guess once I get to it I can shoot some air in there and see what happens.

 

Kewl that ya gave an update.


My truck has a camper shell, and I'm getting some occasional drips inside. I had the camper shell removed to have a piece of molding replaced/repainted and now that it's off I am going to replace my light this weekend.

 

Let us know how it goes. I think mine will be good until I have to replace another bulb in it - might have to pry it off! Speaking of bulbs, that's what happened to mine; I took the truck for state inspection and they found the 3rd brake light didn't work, so they put a bulb in it. The doofus just stuck the light assembly back on with all the trash under the seal. It had leaked before that but not bad.

 

"I could see that the wiring harness had no connections in it and disappeared under the sub-roof." Yes there is a connection, it is just out of sight by a few inches. To get enough slack to hook up the new one you have to 'defeat' the plastic tab that holds it to the cab.

 

Hey, thanks. Maybe I should have had my glasses with me.

 

It rained hard here today and I drove the truck to lunch. No evidence of water in the cab at all. My RTV silicone gasket helper worked. If you do this, take the time to clean the gasket and body. I just used a damp cloth. Set the light fixture as soon as you finish the bead of silicone, put some silicone in the screw holes and screw it down. Like I said above, use a small bead around the gasket. If you use too much it will squeeze out and make it look like a bunch of plumbers were working on your truck.