Hi Stace, and welcome.

I assume you're coming from the UK, so you are spared all the visa agonies. But as Stravinsky said, finding work in France is difficult, particularly if you don't speak the language reasonably well. For doing work as a car mechanic, there's a whole special vocabulary he'll need to understand what's going on - and the local regs on equipment and the "controle technique" (roughly like the MOT in the UK).

Going into business for yourself is an option, but brace yourself for the bureaucracy required to get a small business up and running! There is lots of paperwork, and almost none of it is available in English. Then, of course, there is the usual drill of establishing vendor relationships (for parts, etc.), and handling the accounting and taxes, especially the VAT. If you can do that sort of stuff, there is the possibility of working on an unpaid basis, but having the business pay your "cotisations" (national insurances) as a "spouse collaborator" in the business.

If your French is up to it, one of the best sources for information is the French Service-Public website: SERVICE PUBLIC - Particuliers There are some English pages, but they don't cover nearly as much as the French pages do.
Cheers,
Bev