Recent problem that has me baffled, if I have the lights on with the engine running and attempt to turn the engine off, take the key out and the engine still runs, as soon as I turn the lights off the ignition then goes off. Same happens other way round, no key in ignition and I turn light switch to side lights or head and the ignition comes on. I was not bothered and it's been that way for 2 months or so but I now just discovered as we had fog that the fog front & rears no longer work(neither does dash signal light come on) so it's now become an MOT problem, any clues?

 

p.s Probably unrelated but it started around same time as a fuse blew for the Aux power plug.

I would guess that the current that blew your fuse may have had chance to melt some shielding on your main loom, causing a short across your ignition and light circuits.

It'll be a very difficult job to trace it if that is the case as it could be almost anywhere, unless anyone has a schematic showing where the light and ignition looms are bound together?

Just incase it's a module fault, have you tried disconnecting your battery for half an hour?

Doesn't the immobiliser kick in when the key is taken out? I thought the chip had to be present constantly or is the immobiliser disabled until the ignition is off again?

2 hours ago, Phil21185 said:

I would guess that the current that blew your fuse may have had chance to melt some shielding on your main loom, causing a short across your ignition and light circuits.

It'll be a very difficult job to trace it if that is the case as it could be almost anywhere, unless anyone has a schematic showing where the light and ignition looms are bound together?

Just incase it's a module fault, have you tried disconnecting your battery for half an hour?

Doesn't the immobiliser kick in when the key is taken out? I thought the chip had to be present constantly or is the immobiliser disabled until the ignition is off again?

The immobiliser chip only needs to be present initially. Once the engine is running it's not checked again apparently (a project of mine connected a permanent live feed to the switched side of the ignition switch). All of the ignition switched circuits are bussed into what appear to be two groups.

Have you changed any bulbs anywhere on your car? (Brake/Tail lights especially!!). 

What Focus do you have exactly? There are versions (according to the schematic) that share a rear fog/tail lamp (two filaments in one bulb). An incorrect bulb in here would mean you connect the tail circuit (permanent live) with the fog circuit (switched).