Morning all 2012 1.6tdci titanium x here. Now my dab doesn't work and I'm going to disconnect the battery for 10 mins and see if it resets my non sync sony headunit.  Which battery cable do I need to disconnect first ? 

Why not just pull the fuse that feeds the head unit (entertainment system) ? Less disturbance to other systems than disconnecting the battery. Check which one it is from the manual ( online here https://www.ford.co.uk/owner/my-vehicle/download-your-manual )

 

You should disconnect the negative first.  

But on the Mk3 Focus it's impossible to reach without removing the airbox etc.  So you may as well just remove the positive but take care not to let it (or your spanner) touch anything metal in the process.

As above, removing the fuse might be a better option, but as there are several for the audio system that's not as simple as it seems either.

17 minutes ago, TomsFocus said:

on the Mk3 Focus it's impossible to reach without removing the airbox

Simply disconnect the cable from the earth point on the body above the engine bay fusebox. No need to disturb anything else.

1 hour ago, ianincheshire said:

Why not just pull the fuse that feeds the head unit (entertainment system) ? Less disturbance to other systems than disconnecting the battery. Check which one it is from the manual ( online here https://www.ford.co.uk/owner/my-vehicle/download-your-manual )

 

I've tried that didn't reset anything. Although I didn't leave it long until I put the fuse back in

40 minutes ago, mjt said:

Simply disconnect the cable from the earth point on the body above the engine bay fusebox. No need to disturb anything else.

Do I need to leave it disconnected for a while?

5 hours ago, mjt said:

Simply disconnect the cable from the earth point on the body above the engine bay fusebox. No need to disturb anything else.

I've tried that before and the power was still on, think there is another earth point which is not easy to access.

I now remove the positive lead very carefully. 

On the Mk3 that's the only earth connection to the battery negative.

2 hours ago, mjt said:

On the Mk3 that's the only earth connection to the battery negative.

Only tried on a mk2.

2 hours ago, MarkRS9 said:

Only tried on a mk2.

Yes same happened with me on my MK2, it confused me at first as I expected everything to have shut down by disconnecting it, but it turns out it's designed for jump starting rather than a main earth point to disconnect!

On 3/5/2022 at 8:03 AM, Morty1977 said:

Morning all 2012 1.6tdci titanium x here. Now my dab doesn't work and I'm going to disconnect the battery for 10 mins and see if it resets my non sync sony headunit.  Which battery cable do I need to disconnect first ? 

It doesn't matter which one you disconnect so pull the one thats easiest accessible.

Disconnecting the negative cable from the chassis it will let the BMS still running and active, i do not know it that is the intention or not.