Chris, I'd suggest you get the mouse out of there ASAP, if it's still there (likely is) using baited traps as others have suggested.
Aside from the fowl odor they can create, more from their urine than their feces, they can do major damage to your car itself.
I've heard of them chewing through wiring in the hardest to get at places. Sometimes, all the way through which is actually better as atleast you've got a definite lack of connectivity that can be quickly identified. Unfortunately, they can also chew partially through, leaving you with an intermittant fault that can be much more difficult to find
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Regards, Alan
