New here, but I have done some research on the topic.
My rig is essentially a stock 1988 Cherokee, no A/C, manual trans, a little over 260,000 miles on it (the odometer is broken, so that's my best estimate).

Here's the situation - I live in Northeast WA, so lots of heavy rain/snow in the fall and winter months. I recently noticed a, frankly, ridiculous amount of water pooling at the feet of the front drivers seat. I've had the car for about three years now, and it didn't do this before, and the previous owner (my sister's fiancé) can confirm this never was an issue. The water is collecting on the floor in such a way that I cannot identify where it is coming in from. The floor is soaked, but none of the carpeting going up the side (under the trim or near the center console) is wet, and going up the front towards the firewall is also totally dry. I really wouldn't care except that, with how cold it gets overnight, the water condenses on the interior of all my glass, and then freezes, so I have to scrape the inside of my windshield to drive

I can't imagine it is an issue with the cowl vent (a common suggestion I've seen) as the issue only recently started, but I'm willing to check it again.
The windshield is cracked, but I don't see any moisture anywhere on the dash.
The door is also pretty much totally dry, as is the dash and the seat. The only things wet are the front driver side floor

Recent projects I've done that may have caused an issue:
- Replaced dash gauges (had dummy lights before, installed actual gauges)
- Installed new stereo head unit (had to redo a lot of wiring, including through firewall)
- Moved the heater controls (to make way for stereo)
- Installed new speakers in doors and back
- Redid cooling system (made an open system rather than the closed system)

From these projects, the issues I could potentially see are a torn seal in the door (the thin plastic lining inside) or a missing washer in the firewall.
I checked the door, and all the seals, inside and out, look good, so I don't think its that
The amount of water in the cab, to me, seems like too much to be from a washer, but I could be totally wrong
Possibly something from the vents, I had to move a few to do some wiring/remove some trim from the dash, but everything was reconnected

I am definitely not a car guru, so all of my knowledge is totally guessing. Any and all suggestions (even telling me I'm dumb) is welcomed. Sorry for the long post, figured more info was better than less. I just am tired of the inside of my windshield freezing