First let me start off by saying I am not by any means an electrical engineer and I have little knowledge of electronics.

My problem is my H/K system Head Unit started to intermittently lose power and then after a few days completely died. Head Unit will not turn on. I assume it's something to do with the amplifier and that it pretty much powers the entire system, but I could be wrong.

Potential workaround - I pulled the head unit and tested the battery supply pin 15 (red wire) to the back of the headunit and only getting like 2-3 volts. Weird thing is if I unplug the small 3-pin connector further up the harness that supplies power to the iPod interface and the radio and test the power wire to the 3 pin harness I get 12 Volts? Weird? Not sure why this is? Anyway, I tested to see what would happen if I ran a wire directly from the battery terminal under the hood to the battery pin location 15 (red wire) on my head unit and the entire system came back to life!! Headunit turned on and the audio came through all speakers. As an additional test I unplugged the 3-pin connector and it sent the head unit into "Disable" mode. So I guess this 3 pin connector is also tied somehow to security functionality.

Anyway, what I need to know are a few things:
1) Why would I only be getting 2-3 volts on the red battery wire in the factory wiring harness? Does the amp somehow supply the power via this wire and that's whats blown in my amp?

2) If I hook a fused wire directly from the battery terminal to the battery pin location on my headunit (pin 15 I think) do I run the potential of harm? battery drain? electrical issues?

I really hope there isnt any issues as running a $5 wire is a much better solution for a bad H/K system than buying a $500 used amp.

Thanks

 

First of all. Pin 9 is NOT the battery supply!
http://www.mini2.com/galleries/data/..._hu_pinout.jpg

Pin 9 is the iBus and connecting 12V direct to it is a bad idea. I have no idea how you were able to get the H/K to power on again in this situation.

iBus is a signal that is pulled high through a resistor and pulses low at high speed to send signals. Among other things it carries the steering wheel controls to the HU, and messages between the HU and HK.

You'd need a scope to properly look at this signal, since it's pulsing high and low all the time.

 

My bad, meant to say pin 15 not 9. It was late and I was writing from memory.

 

Just completed the full install with the power bypass described up top and it worked perfectly. I have my radio back!

 

Great! Though still no idea what the original problem was for you.

 

Does the amp have anything to do with delivering power to the head unit? Was thinking that the amp had something blown on its board and was not letting enough power back up to the radio to turn the head unit on, but that is just a guess.

 

No, the original (non HK) car wiring delivers HU power.

If 15 was missing you'd get problems at the HU, no display maybe, even before worrying about the amplifier. Still, fixed is all that matters