Parking in general outside of the main cities is unregulated and you can park where you want. Be careful though for car crime is prevalent so park where your car is easily seen and where you can access it quickly and safely.
Some Mexicans have set up parking on waste land , charging a few pesos for you to park there. This may sound tempting but it's also tempting to thieves. Stick to proper parking garages or on street parking. You'll find meters in the city as well as ticket machines and covered, attendant controlled parking garages. For personal and vehicle safety it's always worth paying that little bit extra for safer parking.
Enforcement of parking is haphazard and only generally enforced when you are causing an obstruction. In that case, you'll find you car has been towed and you'll have to pay a release fee as well as a fine.
Mexico has no concessions for disabled drivers and so most of the time you'll just have to take your chances. Explaining your predicament to a garage attendant often results in a more convenient space in exchange for a few pesos.