I've looked at Michigan statutes and find only one on this subject. Check your citation to verify that this is the section of your criminal code that you are charged with. The only one located is Michigan 750.224(d), which prohibits USE, but not POSSESSION. You should be able to get a copy of the statute at your local library.
If your citation references a different statute, please post it.
Beyond that, possession requires knowledge and if you are in wife's car with the pepper spray in the glove box, arguably you have no reason to know that it is onboard.
I hope this helps.
WEAPONS DANGEROUS-GAS EJECTING DEVICE 750.2241-B 5YR