Truck Repair: Door Ajar light stays on, water displacement, wd 40

Question
Van;
My 1997 3 door F150 door ajar light stays on. It happened yesterday but the interior light did not come on. The next day all was fine. later that day the same problem popped up again but this time the interior light and the lights on the outside top of the cab came on.It's been raining very heavy during these 2 days. I'm wondering if that has something to do with it. Where do I look first to remedy?  

Answer
Hi Roger,
The rain could, because what activates the lights is a switch inside the doors, on the latch mechanism.
It completes a circuit to ground when the latch is open.
If rain is getting past the window seal, and getting the latch area wet, it could complete that circuit to ground, weather the door is open or not.

I would get a can of WD-40, with the plastic tube on the sprayer, and in the area of the latch, just liberally hose it down.
Stick the plastic tube up into any crack or opening you can to hose the latches more.
Close and open the door several times during the hosing.

With the window rolled UP, you can use a plastig item to hold the seal back, and spray some from there toward the latch also.

By the way....WD-40 was orriginally manufactured as a water displacement product, and happens to be the 40th mixture tried, thus WD-40.
Just thought you would like to know.

Van