@NickNack As I learned from experience, steel wool doesn't really work, nor does Brillo pads. Their teeth are so sharp they can chew right thru them and that includes packing tape. Had problem with mice two years ago and it was not fun. The electronic traps that electrocute them do work as long as you can stomach opening them up to discard of the corpse. What I did find that worked was copper mesh that I ordered from Amazon. Comes in a roll and you just stuff it around openings. Supposedly mice do not like the taste of copper. Anyway, it did work for me.
I had my annual check-up for the central air system and when the tech was checking the outside condenser she (yes, a woman tech, neat) asked if I saw her jump back because she saw a mice nest (unoccupied) in the electric box for the unit which is covered but boy give mice a small crack and they will find it.