Rusted Floor Pan

[TheWeldingFords]

While tearing out all of the interior of my 86 f250 I discovered the only rust on the truck.
The driver's side floor pan is rusted quite a bit and I was wondering what the common leak points are of these bullnose fords.

[Gary Lewis]

Yikes!  That's quite a bit of rust.

There are basically 3 ways water comes in:

Windshield: The butyl rubber gluing the windshield in gets hard and cracks, allowing water past it and dripping onto the floor.

Cowl: There's a seal in the cowl area that sometimes didn't get sealed at the factory, and if if it did it also cracks and leaks.

Kick Panel: The cowl for the Bullnose trucks allows debris to enter and it frequently then piles up behind the kick panels.  And that then causes water to come into the cab.  The key here is to pull the kick panel and check to see if that area is blocked.

[mat in tn]

those are certainly the big three but let's not overlook user error. not pointing any fingers haha. just that not everyone wipes their feet. carpeted trucks have the heel pad crack and in neglectful situations wet feet drain beneath and soak up into the padding and often is still wet from the last time etc. rubber floor mats are even worse as many consider them able to be hosed out but again the padding will not dry. especially with a 3'by 5' layer of plastic over it. and so on for 20/years or more by this time. I find the caulking in the cowl to be the biggest issue of all and this allows water to be held in the firewall insulation too.

[ArdWrknTrk]

While you're looking for leaks be sure to check the caulking in the rain gutters above each door.
Cowl drains frequently get plugged with organic debris that divert flow into the cab. (I've pulled these rubber boots completely out)

If you have the interior removed you might want to start at the bottom (lowest spot) and pour a cup of two of water, then go look and see if it appears inside.

[TheWeldingFords]

The passenger side has little to no rust on the floor board.
Could that possibly mean its coming from the rear sliding window?
So far this truck and every other truck I have gotten has either always had a broken or missing latch.

I cleaned up and stripped the entire interior over the weekend and I noticed tons of dirt and debris in the kick panels but they have no rust, its just the drivers side floor pan.
I am gonna replace the floor pan in the future once I have the space to cut out the old one and weld in the new one without getting kicked out of my place.

It also needs a new windshield because its pretty cracked.

[Gary Lewis]

Rear window leakage usually goes to the cab corners, not the front floor board under the feet.  That more likely the other things mentioned.