Steven this sounds like field mice, I see this a lot but its an easy fix. The problem is the little fuckers can fit in any hole that is a hair bigger than their skull so they can go just about anywhere and hide. In a disco they like to nest where it is dry, so in the glovebox, behind it in the dash, or on top of the headliner are pretty common areas.
You could set mouse traps in there, which will lure them out of the nest but can also attract more from outside the vehicle. I have seen mice climb up the transfer case shifter linkage and chew through the boots just to eat a ketchup packet in the console.
Mice nests have kind of a telltale musty odor, you can usually only smell it if the truck has been shut for some time right after you open the door and get in. If you don't smell this then you may be in luck, but if you do smell it then get ready to do some work.
I would take about 3 quarts lemon ammonia, pour it in a poly container and set it in the rear floorboard area. Then pour 2 quarts bleach into the same container and close the door. Wait one hour, then open all the doors and take the container and pour it on your neighbors lawn. Let it air out, it won't take long. In addition to viciously murdering the mice, the odor of the nest should be more or less neutralized so other mice coming in will be less of a concern. There are two choices on how to proceed at this point, you can let the dead mice bodies sit and dry out whereever they lie (a dead mouse will dry out and stop stinking after a while), or you can track them down and dispose of them. The latter may involve pulling the headliner and dash, but if the mice managed to escape the vehicle then the former might not be such a bad option.
Cheers,
Kenneth
