I need help or advice, Please. I have a 77 F250 standard cab 4x4 that somehow or somewhere water leaks in when it rains. It comes in on the passenger side somewhere up under the dash and drains down the fenderwall to the floorboard. Its not fast but enough to start to rot my floorboards until I noticed the water under the mat. Does anyone have any ideas as to where it might be coming in at or how to stop it. Thanks in advance.:confused:

Only a guess, but something lots of guys don't think of:

There should be a water drain on the cowl intake in front of the windshield. If that gets plugged up with leaves algea, or whatever, then the cowl can fill up with water to the point that it runs out the heater ducting, ending up on the passenger side floor.

The drain may be in the cowl itself, or farther back in the heater ducting...possibly from the AC evaporator (which needs a drain too) or under the heater core.

Straightend wire coathanger would be my tool of choice for cleaning these out.

Otherwise I'd suspect the bottom of the windshield.