...and I can't figure out where they're coming from. The Tribute is parked outside at night, windows up and the air intake set at 'inter circulation'. They seem to come at night, leave some droppings are are gone by morning.

Where could they be getting in from? I've done a visual search inside the cab, also outside on the engine firewall, but can't find any holes.

Are there any obvious gaps that the mice can be coming through?

How can you search for these holes/gaps - using something like a shop lamp, either in engine compartment or underneath vehicle, and look for light shining through in the cab?

THNX