2005 Mazdaspeed Miata Stereo troubleshooting

Short version: OEM Bose radio in my Miata randomly seems to lose power in the past couple days. Fuses are good. Plug in back of radio is securely plugged in. What do I check next? Wondering if this is going to be an interconnecting wiring easter egg hunt or if the head unit itself is just dying.

Long version:

So, the last two times I've driven my Miata, the radio has suddenly stopped working at some point. The symptom is that the head unit goes completely dark like there is no power to it at all. No buttons or knobs have any effect on it. Turning the car off and back on does not fix it. The first time this happened, it came back on after about 5 minutes or so. There was nothing that I noticed in terms of a large bump or pothole that coincided with it going off and coming back on. Today, it happened again. When the radio is gone everything else on the car seems to work just fine.

I was a bit worried that there was something more sinister going on that may affect other electrical items on the car, so I investigated a bit today. I checked the radio fuse in the inside fuse box and it was good. I checked the radio fuse in the engine compartment fuse box and it was good. Both fuses seemed fully seated in their sockets.

I removed the radio thinking that the plug might be loose after 11 years. It seemed ok. I plugged it back in and with the radio still out of the dash tried it out and it worked. I reset the time and a radio preset. Then I installed the radio. When I started the car the radio went dead again and remained dead for the 10 minutes or so I was messing around with it. I ended up removing the 20A fuse in the inside fuse box since it only powers the radio.

So, what is going on here? This is the OEM Bose radio with built in CD changer if it matters. I would think I could eliminate the separate amp as the problem since the head unit would still power up. Not sure if I all of a sudden have some electrical gremlin in the wiring between the fuse box and the radio or if the head unit itself is dying. Any ideas on the next troubleshooting step? I don't really want to get an aftermarket radio if the head unit is the issue. I would probably get a used OEM radio from pick-n-pull or Ebay before I went aftermarket.

EDIT: Oh, one more tidbit. I will be driving the car to the airport where it will sit for 7 days, so the next opportunity I'll have to mess with it is probably Halloween.

So, since the radio forgets the time and the station pre-sets it seems like it is losing both the +12VDC from the battery as well as the switched +12VDC from the ignition switch.

I didn't check the room fuse, but the interior light still works when the radio is dead, so it must be ok.

I guess if the ground wire from the head unit is only making intermittent contact then that may explain the symptoms. I didn't look for it, but I assume it is somewhere behind the radio. I'll try to find and follow the black wire and see where the ground point is located.

Hello, is this thing on? Did I get shadowbanned? This forum answers all questions, usually in minutes. Three days and this thread is just me talking to myself.....

Seriously, does anyone have any thoughts/ideas/insights to help me figure out my stereo issue?

The BOSE in my 06 NC started the same issue, or it would just start crackling. SOmetimes it would do it non-stop, sometimes it wouldn't do it for a week.

That plus a leaking, fading top meant I ditched it.

At least on the NC, replacing the head unit meant a bunch of other stuff to do as well. And having the top professionally done with a quality top was $1900.

I couldn't bring myself to spend $3k+ on the car. Although now I wish I had.

The CD changer in my 2004 MSM jammed up, so I feel your pain. FWIW, the radio still works (and I so enjoy listening to commercials ). Have you pulled the radio and checked continuity of the ground wire to chassis and whether it has 12v at the power wire when it fails? I'd try to isolate whether the issue is wiring/ignition switch or radio first. I have a factory shop manual with wiring diagrams if you need any wires traced down. I'd say check mazda-speed.com, but they are moving to a sub-forum on miata.net, so maybe check there.

Get it in a non-op condition, then check the power feeds to the back of the stereo to see if they have 12v.

Next time it happens, stick a voltmeter on the cigarette lighter output (while the car is running) and see what the system voltage is. If the alternator is stuck on full output it's possible to raise the system voltage high enough (like over 15 volts) that the radio will refuse to run.

You tend to get weird gauge behavior with that as well, fyi.

Wait, you have a MSM... and you actually turn on the stereo in it...?

I sid not notice any strange gauge behavior when the radio was inop. I'm thinking that the ground wire connection or an internal to the head unit intermittent fault of some sort is the issue since I seem to be losing both the switched 12V as well as the always hot 12V at the same time.

I will try to pull the radio while the problem exists and check both 12V inputs. When radio is out I will find the ground point and check it.

I have the wiring diagrams.

Thanks for the respnses.