How to take apart radio?

Since you do NOT know what it is hooked up to, AND you DO know that: "When I press it, something in the engine compartment seems to spin into life...", why not have a friend hit the switch while you have the Hood up and you're looking in there, i.e. Without the engine running or set to run.

It's not too much of a precaution and it ~might~ save you some repairs.

Or force yourself to trace the wiring to it's components.

FWIW

E