Help wanted - audio signal

[RaKid]

Recently upgraded the two front speakers in my GC8. Found some wiring was miss-matched so cut the head unit-to-oem plug loom up and re-soldered every wire, pin for pin correctly. Tested, all OK. Fade and balance all working now correctly. Bass and treble gains all working etc.

 

Car went away to get painted and came back with the head unit powered on but no audio. This was about 2 weeks ago.

 

I finally had some time to pull everything apart today to start investigating.

 

Put a 1.5V AA battery on the speaker to confirm it works - it does.

 

Checked the loom wasn't damaged in any way- no damage.

 

Pulled the front speaker out and plugged in rear of car where I have vacant speaker slots with existing OEM plugs and plugged in. Still no sound.

 

Played around with fade and balance. Checked mute button. Tried different audio sources, etc - nothing works. No sound at all or even vibrations.

 

Check the power fuse on the rear of the head unit. It's fine. (I mean, obviously, because it powers up).

 

But, I'm now at a loss.

 

I get a 6 volt reading on the front and rear plugs both pins - but what does this mean? 

 

Old fella recons I should patch my speaker in directly after the head unit plug on a pair of speaker wires and if there is no audio then he recons the head unit it toast.

 

Any help appreciated.

 

[RaKid]

Found the issue.

 

Measured each speaker wire's resistance at the loom behind the head unit and both + & - LHF speaker had 1-4 Ohms but should have been open circuit. Pulled speaker and found tabs bent. Bent back and refitted speaker and all working now.

 

Looks like the internal amp shuts down if it sees an earth in the speakers. 

 

Problem solved.