Can you polish your guitar with car polish?

I wouldn't say that's a good idea. You should focus on using something that will not damage wood. Car polish may end up damaging your guitar.

ANSWER

In general the answer above is 100% correct. Also I have heard that you shouldn't use furniture polish either. Why? I don't know but I don't.

But I have been using Blue Coral out of a squeeze bottle on my guitars for 30 years. This was a tip a guitar builder gave me many years ago. Strats, Tele's, acoustics, and Mandolins all get the Blue Coral. It is mildly abrasive and can take out some minor pick marks and things like that. (Many other car waxes are highly abrasive and that's usually where the trouble begins. Your guitar finish will end up with swirl marks.) And it leaves the guitar in terrific shape. Don't use to much, use a damp cloth when you put it on, let dry, and use a soft dry cloth when polishing. I generally polish them about every 3-6 months depending on how much I play a particular guitar. You don't want to over polish them either. In between polishing just use a soft clean cloth and wipe them down real good. IMPORTANT: Never use this wax on a rosewood fret board. It'll get in the little grooves and be a real pain to get out without damaging it.

If you can't find Blue Coral try a Turtle Wax (squeeze bottle again) that is also non-abrasive or mildly abrasive. I use that to now since my Blue Coral is almost gone.