I have rain water getting into ventilation system then leaking onto floor on passener side

There should be rubber drain plugs under the car's carpet (I believe the Lincoln has screw in ones)look under car and pull the plugs and let car dry out completely replace and seal the plugs and any other pin holes you might have in the floor also I believe the fresh air intake when malfunctioning will allow water to fill in car when driving in rain (should be on rear right side of car water will come into if fresh air intake is not working properly (

You need to find the conduits for rain - one of them has a leak in it probably from corrosion. Try to locate just where the water is getting in and see if you can use a sealer to stop the water from getting in.

I would remove the glove box and anything else in the way and look for the source when hosing down the car.

it is leaking from the outside air intake there is a hold there to clean it on on the passenger side top grill by windshield ask me more will explain

Ac hose leak?
leaking heater core?

Hint: it leaks when it RAINS

If it were related to the heater core or the AC drain, it would be leaking when it is not raining also, so those diagnoses are not logical.

The grand prix has a long history of floor leaks from seal failures around the air intake under the windshield cowling, where RAIN water runs in.

check windsheild and fresh air intake area at rear of front hood for leak/ seal prolems. Also door weatherstipping , rust should be a problem yet but that depends on your physical location

there may be some body rust around the window seal or in the air intake area, depending on your climate, condensation can sometimes drip of the AC system onto your feet

It could be a plain old fashioned leak around the windscreen - difficult to find but try sitting in the car while somebody plays a water hose over the windscreen.

It could also be a blocked drain in the ventilation system - fresh air is normally drawn in to a car via vents at the bottom of the windscreen. These vents normally lead to a "box" like structure where any water that enters the vents drops to the bottom and then drains away via a short hose that runs to somewhere underneath the car.
If the drain outlet or hose gets blocked (by leaves for example), it can cause the box to fill with water to the point where it can leak out in to the passenger area.

Hope this helps you find the problem.

Water is probably from the fresh air intake located just under the right plastic cowl (lower windshield reveal molding). We see this often in our shop. To access the fresh air intake, remove the right windshield wiper and then remove the screws fastening the cowl to the car body. Remove the right cowl. Just above the rectangle shaped fresh air intake (& cabin filter) should be a bulb shaped strip (approx 12" long). All too often, this strip comes off and no longer diverts water. Glue the strip back onto the firewall above the fresh air intake using weatherstrip adhesive. Reattach parts that you removed and now the water should be diverted to either (or both) side(s) of the cabin filter. Good luck

The heater/airconditioner box under the dash has a drain hose to allow condensation to drain when the air conditioner is running. If this hose gets plugged, rain may accumulate in this box also (if it's raining heavily), as it comes in through the fresh air intake.

Look on the engine side of the firewall, probably on the passenger side, for a hose coming through the firewall that is not connected to anything. It is usually short, has a 90 degree bend, and the open end is down. Make sure that the end of this hose is not plugged.

It could be coming in through the rear door as the rubber might not be sealing properly the easiest way to find the leak is to remove your seats and carpet sit inside get someone to squirt the car round the doors and windscreen air vents.