A bit of an update for you from my side... First I tested all my fuses for a 6th time, then checked the harness and everything checked out fine. However, last night I drove out to meet someone with an 8 and we swapped head units.

My origional = Dead in his
My replacement = Worked in his

His working = 5 blown fuses in mine.... (The room fuse (very bottom) in the kick pannel)

I am completely at a loss, so I think I am just going to suck it up and take it to a shop and have all aftermarket installed.

Ya, my LCD/head unit has some issues too, kind of the opposite of your problem. All my dials and everything works.

Pics:
https://www.rx8club.com/rx-8-discussion-3/radio-stereo-lcd-display-problems-contrast-198309/

So I finally got around to taking my doors apart to test the side Bose amps and I can confirm that its not the problem.

I'm completely stuck as to what the issue is. I'm probably selling the car sometime over the summer anyways. I can't even think of a way to diagnose the problem so it would probably cost a fortune to have the dealership figure this out. I'll just eat the lost value when I sell the car.

EDIT: I was at Best Buy today chatting with the car audio guys and they said they can test the harness & speakers for a potential short for only $20. I set up an appointment for next friday. I'll update on what they find.

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I'm having a similar issue on my 2004 non-bose. The radio stopped working. The LCD no longer displays anything. My AC and heat still work. I purchased a used radio from another member and the issue is the same. I've checked every fuse. I've completely disassembled the radio and reassembled it. I'm at a loss.

I took my car into Best Buy and they checked it out. They told me that they are sure there's a short somewhere, but it would be near impossible to find. The power supply is fine up until it reaches the actual head unit.

I know it's not my amps shorting. How can I diagnose where the short is coming from? Can I take the wiring harness completely apart and only plug in the ground, Constant 12V & Switched 12V wires? If so, would I do this by just 'snapping' the plastic pieces off of the harness?

Pardon my ignorance...I do not have a shop manual or anything but I was wondering something. I have pulled everything out again and noticed there is a lot of electrical tape around my wiring working back into the car which makes me think someone got into it and was hacking away splicing and crap I plan on pulling all of it off and checking the wires and such but if I cannot find the short in my system does anyone know how the wiring is setup in the car running through the dash? is there a harness it originates from or is it all hardwired in.

My thought is just if I cannot find my short in the system can i simply purchase the wiring from a parts car and simply re-run the wiring without much of a problem or is it hugely more involved than that? I know it sounds desperate but it is killing me having to use my iPhone for music in the car with a nice system that is there just non fuctional.

The wiring harness that comes to the back of the radio is wrapped in electrical tape from the factory. Ordering a complete wiring harness for the car would involve you stripping the car to install it as it really does run everywhere.

well...good news and bad news i guess...honestly I had kinda hoped that the previous owner had tried something as it probably would have made finding the short easier. But I guess it is good to know that he wasnt messing with things that he shouldnt have. I am just not used to seeing electrical tape from the factory i guess.

I had Mazda look at my car. They're telling me the audio control unit is broken and needs to be replaced. The part is $600. Anyone know where I can find one of these cheap? :(

there are a couple cars being parted out in the ForSale thread.

I want to say I just saw a bose headunit as well in it's own FS thread.

What exactly is an audio control unit? It sounds like what the installer was saying went bad in my car. ( does anyone have a diagram that shows location etc?)

Bump..any results to this thread? Same problem..

They replaced the audio control unit and that did not resolve the issue. I still don't know exactly what that part is. When i asked for the part number they gave me the part number for the radio itself. They told me they would need to order more parts and call the tech line. I haven't taken it back since then. I'm annoyed that they can't figure it out.

Pretty sure i'm just going to go with a Metra kit after reading all of this

Has anyone solved this yet? I'm not sure but I think it might have more to do with the battery. I bought a Optima Red Top and installed it yesterday. I also added a disconnect switch to the negative cable and put a new terminal on the other. Seems like everytime you play with your car you gotta disconnect neg cable and I'm hoping this will be easier than removing it every time. All this meant some wiggling even thought I tried to be easy. When she started right up but I don't have radio or temp display now. I've been looking online for solutions and while alot of people were working on their audio units when this happened there are some who jumped/changed/disconnected the battery and when the car was started the display was out. I'm checking my battery connections tomorrow. I have a feeling it is in the harness?/wires by the battery.

seriously i'm having synchro problems and i just literaly parked my car for an hour, got back in it and plugged in my ipod and my headunit wasn't working. the radio itself works on am and fm, but you put in a cd and it doesnt play the cd and the cd button doesnt work. I'm about ready to sell the god damn thing and i just put full turboxs exhaust on it

What's that got to do with this thread?

Try and focus.....

Disconnect negative battery cable for a few minutes then reconnect. Sometimes disconnecting the battery, jumping it or a new battery will screw up computer system making the car think it is being stolen.

yeah i tried disconnectiong the battery last night, woke up this morning and reconnected it and it still doesnt work. it also kicked on the loss of traction light and the dsc light was flashing. had to drive it down the street and back, shut it off and start it 3 times before they stayed off. cd mode still doesn't work, even if i put a cd in. only thing i can think of is maybe the lint in the bottom of my iphone shocked it somehow and somehow fried it.

Traction and DSC came on because you disconnected the battery and then didn't take the stearing wheel to the left and right fully.

ahh i see, well thats simple enough, anyone know of what i could do for the cd player, i had it apart. didn't notice anything. checked all connections, everything works except the cd button and putting a cd in doesnt get it rolling either. So i'm not so sure its just the faceplate lost contact with the button or whatever behind it because you think putting the cd in would still start it. so i found a used one with 100 percent satisfaction guaranteed on google, think its worth the try? or pull the circuit board out of the faceplate

What happens when you use the mode button on your wheel? Im pretty sure that switches from one source to the next...I could be wrong though...I never use the button.

it just cycles it through am and fm. im going to rip the face plate apart tonight i believe to see whats wrong

So I've still been unable to diagnose what is wrong with my radio. The audio shop I had it checked out at said my only option is to replace the stock head unit with metra kit as well as every speaker and all of the amps. They said that one of my speakers might be shorting the head unit and it's not possible (or too expensive) to diagnose what speaker is causing the short. Does this sound right? The said if I just replace the head unit with a aftermarket I could have the same issue I was having with the 3 BOSE head units I've tried. I mean if I HAVE to I suppose I will buy all new speakers, and amp, a sub, head unit, metra kit, and pay for an install. But I wanted to double check if anyone has a better suggestion before I spend a few grand just to get some music in my car :sad: ....

Thanks for anyone that has a suggestion.