When it rains, the back wall of the cab somehow gets wet. Im speaking of the far rear of the cab behind the seat. Somewhere in the insulation I guess? I dont see it running down the window from the roof. It guess its where the back window goes into the cab of the truck? Anyone else have this issue before? Where do I began to fix this?

 

I'd check to see if someone had a wall-mounted amp(s) in the past because they drill through that back panel of the can and of those screws are no longer there, they may be holes. Also might be plugs/seals missing? I think the amp is a long shot, but that's all I got.

 

3rd brake light is leaking.

 

that may possibly be it. Never thought of that. I assume the rubber seal may have corroded or isnt secured tight anymore. Thanks. Ill check it out.

 

3rd brake light or rear window

 

I had the same issue. Both my 3rd brake light and window seal leaked. I have a sliding back glass and got it all replaced for around $300 give or take a few bucks.

 

I had the same problem. It was the window seal. I removed it and put in some new butyl seal. It is just a matter of removing the trim, spraying with a hose to verify where it is leaking then unbolting the window.

 

What year truck? Slider or solid?

The rear window is a unit which bolts onto the cab. They can either leak where the window unit meets the cab (easy but tedious to fix), or the older sliders can leak through cracks in the window unit frame (difficult to impossible to fix). Ford redesigned the sliders somewhere around '02 to fix the leaking window unit problem.

In my opinion, it's less likely the 3rd light is leaking as I believe the only entry into the cab is a rubber plug with a few wires molded into it, which is unlikely to be displaced.

 

I interpreted "not seeing it from the window" as is not being near the ceiling at all. If it's around the third brake light area, it's likely that.

 

I swapped my original solid window for a brown tint slider from a '97, only to find out it leaked due to a cracked frame. Fortunately I live in California and it never rains here, so it's not really much of a problem ...