Cruise Control
 

So, I didn't properly shield my cruise control cable, and I melted it. So I bought a new one from Planet Miata. I also bought the actuator.

I installed these things, and my cruise control still doesn't work. What are the other parts of the system, and where can I find them on the car?

For what it's worth, the automatic volume-with-speed thing stopped working properly at about the same time I melted the cable (coincidence maybe?), so now that function only works when the cruise control system is on.

Any ideas on what I might need to do to fix this problem?

What always bites me is the little rubber stopper thingy on the pedal arm (brake or brake and clutch both...can't remember). Make sure yours haven't fallen off or otherwise gone missing. they look like a little button made of rubber. First time I lost one I didn't know what it was and threw it out thinking it must be some part from a toy or something.....

What's the switch at top of clutch pedal? - MX-5 Miata Forum

(hope that link is allowed...)

Would that explain why the audio adjustment only works when the cruise control is switched on?

my gues is rpm signal snafu
the cruise just monitors the vac and maintains it.

What do you mean rpm signal snafu? How do I test that?

somewhere the system picks up a rpm signal as reference for your radio adjustment etc find that and you will likely find what is wrong.