"Wouldn't calibrate"......not sure what that means.
Could be "too much metal", could be something else. How old is it?
Do you have another compass to check accuracy with (away from the jeep)?
If yes, how many degrees is it off?
I think car compasses (generally made to be around some metal) are only sufficient to give a general direction, maybe good to 8 points of the compass, or a little better depending on quality and magnetic declination (that depends on your specific geographic location).
They certainly aren't made for real navigation, but they do look old-school cool.
Good luck!