Classic/Antique Car Repair: 66 Mustang Water leakage, air plenum, squirt water

Question
I bought a 66 mustang about a month ago. When ever it rains it leaks water, mostly on the drivers side and a little on the passenger side. It drips on the left side above the parking brake. I was wondering if you knew how to fix this or know what the problem is.

Thanks,
Matt

Answer
There are three possibilities:  One is that the rubber seal around the windshield is dried out and shrunk, in which case the water is coming in under the dashboard and running down the wiring to where you see it. If that is the problem, you can find it by having someone squirt water at the edges of the windshield while you lay on the floor with a flashlight to see where it first appears.

The other possibility is that there is a hole in the air plenum in front of the windshield.  You can check for this the same way - pour water down into the openings in front of the windshield to see if any gets into the car, and where it is getting in. - you'll have to get a body man to remove the grill in front of the windshield and take a look in there for a rust hole or a plugged drain hole.

The third possibility, if it only happens when you are driving, is that there is something missing in the front end sheet metal that is letting tire splash hit the firewall, and the resulting water is leaking in through the holes in the firewall.  This would only be if there is something missing from the inner fender and splash shields - and the car would not leak when it is parked.

Dick