Yet again another Rear Fog

Morning Folks,

Unfortunately the '89 Cabrio we have failed its MOT yesterday, very frustrating to say I've spent the last year putting her back together. Basically its only the rear fog were having a problem with, so i'd re wired the bulb to another switch and the mot'er said it had to fail because the switch wasn't labeled as a fog light switch. I know the bulb works because when i flick the switch I've fitted it comes on.

Because of this silly technicality I've decided to try and get the genuine switch working. I've got my hands on another switch and it still doesn't come on. Then came out the trusty voltmeter. I have power going to the switch from the lights as the switch illuminates however when putting the volt meter on the others wires theres nothing (two yellow/white and one grey/white). I've also checked the fuse at the top of the fuse box and that is all fine, my thoughts were should there be a relay for it?

Could someone please point me in the right direction.

Regards Richard + Jane

no relay for the rear fog, only fitted if its got front fogs.

basically the grey/yellow wire should be live as soon as the headlight switch is on 1 or 2 clicks. (actually it might be only on the 2nd click on pre-90  and/or rear fog only cars looking at m,y diagrams) this is the power input for your foglight switch. the grey/white on the back runs to the rear fog fuse, the yellow/white is for the front fogs so dont worry about that.

if there is no voltage to the grey/yellow then trace this back, worst case jump it with a lights on or ign live feed somewhere and you should be sorted. quick n dirty test is to find a live and stuff the wire into the back of the switch. if fogs then work you know you're good to go

I've completed your tests and discovered that from an ignition live the light will come on, but there is no power from the grey/yellow when I've bridged it with the grey/white. What would your suggestions be?

grey/yellow wire should be live with the lights on, if it isnt you dont have a feed from the light switch. follow the wire back to the fusebox and see if you can find anything obvious.

if you do have power to grey/yellow but putting a feed onto the grey/white woint bring the light on then you have a wire fault somewhere. put a live feed to the grey/white at the switch then check at the fuse, if you have power there then the switch wire is ok. then its just a case of workjing from there back!