The head unit energizes the blue wire when it is switched on (the blue wire is an output from the HU, not an input). With power supplied to the red and yellow wires and the ground grounded, it should work. The only thing left to try is disconnecting all the other wires from the HU, because sometimes a short in the speaker system or possibly the blue wire will cause a HU to shut down completely.

 

Well I didn't try disconnecting the speaker wires or double checking the ground by manually grounding the black wire. It's out of the car now so I'll hook up my 12v ac to dc converter and seeing if I can get it to light up.

 

Well I saw a Pioneer HU on Craigslist cheap and was thinking of picking that up. While I was waiting for the guy to get back to me I thought I'd better do the last double check on the current unit. when I hooked it up and tried to turn it on it finally came on intermittently while I was jamming it's buttons. The faceplate to HU connectors were failing. Shining them up with a wire brushe fixed it. Works great as a radio. I am not sure I have any of my tape collection left but it sounds good. Needs rear speaks and an amp etc etc etc.

Thanks MK & hatchback

 

I was having the same problem with my faceplate on my Sony headunit. I run an AUX cable from my iPod to the front of the stereo. Randomly, the faceplate would go dead and the music would stop (appearing to be off), but it turns out the faceplate just wasn't getting power... and as a result the music stopped playing since it was plugged into the faceplate and had no way of transmitting data to the headunit with the bad connection. Too bad it (the faceplate turning off) didn't happen while listening to FM or a CD... I would have identified the problem right away since music still plays through FM and CD when the faceplate is down (it folds down to put a CD in).

When I figured out the problem though, I felt extremely relieved... I did not want to spend money on a new headunit. lol. I like the one I have just fine, I just need it to continue to work right.

 

It likely would have gotten me on track a lot faster if I would have dropped a cassette in in the first place. That's the problem with micro electronics. Your jack would probably never have failed if it was a stereo 1/4" phono jack!



EDIT: Oh, now I see that it was the bad faceplate connections that were cutting out taking the Aux in with it. I use the same arr with my HD HU in my Bonneville. Jump it in with 1/8" stereo jack into the front of the faceplate. Sticks way out and looks awkward. Maybe an right angle plug would be helpful.