A visual inspection is usually sufficient to diagnose whether this is the culprit.
Back truck window leaking.
Water may be present on or under the carpet.
If the weatherstripping is not 100 replace it.
Take your screwdriver and gently pry the rubber window trim away from the windshield near the source of your leak being careful not to bend or nick it.
Also inspect the bottom of the windshield s glass for nicks chips or cracks.
The rubber seal around the edge of the door can also sometimes be a cause of leaks.
On some models a void in the rear window seal may cause a water leak.
The back slider windows on some older truck models have a tendency to leak.
When water comes in around the glass it can become a big problem for truck owners.
Finding windshield leaks to test for a leak vandale recommends gently showering the car with water.
If the seal gets damaged or dries out water will track down the front of the door and into the car.
If a hose is put on full force the water will bounce right off.
284 people reported this problem.
The lower the water pressure used the faster the vehicle will actually leak he explains.