I HAVE A2005 V6 MUSTANG AND TWO WEEKS WE HAD A BAD RAIN STORMAND IT STARTEDLEAKING IN THE PASSENGER SIDE UNDER THEDASH.THE NEXT DAY I WASTRYING TO GO TO LUNCH AND THE CARCRACKED BUT ALOT OF THE ELECTRICAL THINGSDID NOT!
I TOOK THE CAR TO THE DEALER AND TOLD THEMWHAT WASGOING ON.I CALLED THE DEALER TO SEE WHAT THE PROBLEM WAS, AND THEY SAID THAT THECAR WASWORKING FINE, AVERY THING WORKS. (LET ME TELL YOU THAT CAR SET OVERTHE WEEKEND)
SO THE ONLY THINGI CAN FIGURE IS THE CAR DRYEDOUT. FIXEDIT SELF. I TALKED TO FREINDABOUT THIS PROBLEM AND HE THINKS THAT THE HEATER BOX DRAIN IS CLOGED IN SOME FASHON ? AN JUST THE OTHER DAY IT RAINED AGAIN AND ITLEAKED FROM THE SAME PLACE DIRECTLY IN THE MIDDLEOF THE PASSANGER SIDE FLOOR . SO I GUESS IT OFF TO THE DEALER ONE MORE TIME.!!!!!!!!!!!!

 

grrr feel the wrath of caps lock all shall bow down......................i thikn the heater crap is in that area dealerships wont help most of them have HS kids working for them take it to a reputable local speciality shop if you want it fixed right IMO

 

Any possiblility that there is a leak coming though the lower part of the windshield? Seems rare for a newer car, but I had a 91 Eagle Talon TSi AWD that had a serious leak from the front windshield. I ended up withwater all the way to the back floor.

Maybe an auto body shop could find the problem. Or at least get someone at the dealership who really wants to take the time to find the problem. Don't put up with someone just saying there is no problem. If there wasn't a problem, you wouldn't have brought the car there in the first place.

 

This is a common problem from the 2005+ mustangs. There is a technical service bulletin for this problem. The dealership knows what the problem is and needs to fix it. Head over to the 2005-2008 section and ask about leaky mustangs, you will get a lot of replies.