Mice!

[PaulZ]

In behind the fenders there are flaps of material that allow the water to run out of the cowl area.
Also look closely at the transmission floor shift area.
Make sure the door seals are attached properly .

Thanks. Can you see or get to those flaps?

In any case things are looking up. Four nights at the cabin without a mouse since I plugged the wiper holes with rags. I can't imagine how they can even get up there without sliding down the fenders. Also I read that with the heater controls off there is supposed to be a door that blocks outside entry.

Door seals look fine as does the trans tunnel.

 

[RonD]

Good stuff on the 4 days no mice

Its a vacuum operated door that should close and block off Fresh Air Vent, used in OFF and MAX AC settings
But with engine off, and no vacuum for long enough the door would be open most likely, as its Default state(no vacuum) is open
Its under the glove box, has a white vacuum hose hooked to vacuum motor and a "T" with another white hose that runs to the firewall and out to Heater Hose Bypass valve, grey vacuum hose in engine bay, just FYI

Try to remove any short sticks around the vehicle, as the mice can use those to pole vault up onto the hood

 

[4x4prepper]

Check your shifter boot if you have one and go under the vehicle and see if they have eaten through the rubber plug (at least on my 1980s vehicles) for the seat belt warning wire. I think on a 1999 you have a rubber boot over the steering shaft where it enters the cab.

I have watched a mouse being chased by my cat run up a brick wall 8+ feet and then run upside down on a painted horizontal soffit, and go into a vent. The cat did chase him until he did the soffit thing. Besides jumping (just googled it - 13 inches), they can drop a decent distance from a tree onto your car. Getting to the wipers would be no big deal, as my cats walk up my windshield all the time and that is pretty smooth.