Yesterday I was driving home from work running the AC and listening to the radio. Suddenly the radio went off and I smelled an acrid smell. I turned off the AC, opened my windows, and after a few minutes the radio came back on and the smell went away. Later that afternoon (after I had been home about 30 minutes), I had to run an errand and it happened again. Today I had to move my car to weedwack the driveway, and I turned everything off before I turned it on to see if the smell would reappear. It happened almost immediately. I opened the hood and it seems to be coming from the passenger’s side near the power distribution box or the brake fluid bottle. I can’t really identify it. I drive a 2003 Mustang, V6 engine. Has about 70,000 miles.
This would probably be a short circuit that is not protected by any fuse. The circuit may be protected by a fuseable link but the current being drawn is not up to the level to burn the link out. Also consider that there may be bad (ohmic) connection that is feeding a high current load.
Somewhere there is heat being produced that is burning insulation so have an electrical technician look at the system, especially around the power distribution box, to try to spot the problem before you have a full blown car fire.
Hope that helps.
I should add that I drove around for two days with the radio off but everything else running as usual (with the AC on for a while, too) and there was no burning smell. So my guess is it is a short in the stereo/radio.