Wiring difference between head unit and speakers

nikos · 21-01-2025, 08:10 PM

Hi all.

I'm trying to get to the bottom of a problem with a 2011 Focus. The speaker wires that come out the back of the head unit differ in colour to the speaker wires in the door - this leads me to believe that somewhere between the head unit and speaker there is an intercept or some other circuitry.

The problem I'm having is no sound. The head unit and speakers are all tested independently and working; just not when connected together through the factory harness.

If I power up the head unit from a nearby external power source (not the car), jump wires from the HU to the speaker wires in the dash, I get sound. However, if I plug the HU straight into the factory harness and turn the key on, I don't get sound. This leads me to believe the car is doing something funky between the dash and the speakers in the doors.

Can anyone shed light on this?

Cheers, Nic

foxtrot3 · 22-01-2025, 08:17 AM

Hi. Was this head unit working in the car and then stopped working or is it a new install? If a new install did it work with the old head unit? It may have an amp that will need a trigger from the head unit or you may have a short in one of the speakers which will put the new head unit into protection mode. Cheers MD
PS: amp turn on may be purple/red. MD

nikos · 22-01-2025, 10:45 AM

Thanks for your reply foxtrot3.

I'm upgrading the original Ford HU to a new Chinese Android one. There was no sound with the old one, hence the upgrade.

When I first plugged the new one in with supplied harness, everything worked perfectly for about 2 minutes, then sound suddenly stopped. After I disconnected and reconnected the battery, unplugged and re-plugged the harness it worked again for a short time before failing once more. Since then I have not been able to get it working.

There was never any crackling or popping, the audio was simply there or not - which led me to believe that the wiring was ok but maybe ecu intervention or something.

Do the speakers wires from the dash harness go directly to the speakers in the doors? Or do they go to another amplifier or controller first?

Cheers, Nic

Honest Gaza · 22-01-2025, 12:25 PM

Could be a long shot but is it possible that the Car Battery needs replacing ?

A Couple of years ago my Renault wouldn't fire up the Stereo and Amp (everything else appeared ok). I had noticed intermittent issues with a slow start of the Engine but assumed it was just an indication that the Battery was on its way out. Decided to change the Battery and everything has been good since then. (All the start-up components must have decided...nah, it ain't happening).

nikos · 22-01-2025, 01:08 PM

Thanks for your input Honest Gaza. The battery is new and in good shape. Cheers

foxtrot3 · 22-01-2025, 05:08 PM

Hi. Check each speaker wire for a short to earth and check the resistance across each pair of speaker wires using a multimeter. All speaker wires should be open circuit in respect to earth and show somewhere between 4 to 8 ohms between the positive and negative wires for each speaker. Cheers MD