water leaking into cab- how to chase the source?

[pybyr]

I am noticing that when it rains, I seem to get water coming into the cab from behind/below the rear window on the driver's side

Rear window is the original factory non-slider.

No visible faults in the gasket based on a quick look.

Truck does have roof marker lights (factory OEM) and a roof-center aim-able spotlight (it's a former fire truck); there is some rust in the metal headlining near where the spotlight goes through. I don't know if water could be coming through and then running backwards and down? (this seems to happen more noticeably when parked with the front end lower than the back).

Can anyone suggest any tips and tricks of known possible causes or tips and tricks to trace where the water is entering, so I don't have to do a random wild goose chase?

Thanks!

 

[jwalterus]

yay! I had that fun in my old truck, guess what you get to do?

remove all the trim panels from the rear and take it through a carwash!

it's what I did anyway, if it comes from under the headliner, your clearance lights are probably to blame

 

[dmaxjoe]

Mine was the cargo lite over the back window.

 

[MIDNIGHT RIDER]

I am noticing that when it rains, I seem to get water coming into the cab from behind/below the rear window on the driver's side

Rear window is the original factory non-slider.

No visible faults in the gasket based on a quick look.

Truck does have roof marker lights (factory OEM) and a roof-center aim-able spotlight (it's a former fire truck); there is some rust in the metal headlining near where the spotlight goes through. I don't know if water could be coming through and then running backwards and down? (this seems to happen more noticeably when parked with the front end lower than the back).

Can anyone suggest any tips and tricks of known possible causes or tips and tricks to trace where the water is entering, so I don't have to do a random wild goose chase?

Thanks!

First suspect is that spot-light.

Take it loose and thoroughly clean it's mounting-base along with the area of the cab where it mounts.

Apply a layer of good silicone sealant, covering all holes, and re-install.



Second suspect is the 20-year-old plus cab-lights.

Most likely the lens are badly sun-cracked and letting water through, plus the base gaskets may be loose or torn.

J.C.Whitney has for sale a direct O.E.M. replacement set of five that are an almost exact match to the originals.

I put a set of these on my truck a few years ago and no leaks so far.

I applied a layer of silicone sealant between the cab-light bases and cab-roof.



Third suspect, IF you have it ( I don't ), is the cargo-light.

The same method of sealing goes for it as for the spot-light.




If water is running inside the rear wall when it is lowest, then it is also running down the A-pillars and soaking the carpet under-layment.


When you get the leaks stopped, remove the carpet and pad and hang them over the fence a few days, while you clean, dry, and rust-proof the floor.

 

[plywood]

Mine was leaking down the pillars between the windshield and the doors onto the carpet.

I resealed the windshield and failed success.

Turned out it was simply the caulk/grout like stuff used at the top of the pillar where it meets the roof. Just a small crack and seemed like more water then possible was coming in.

Seems to me the rear has the same seam.

However I don't have extra lights so that could certainly be the culprit.