i compared the switch with the rear fog light switch, the relay i don't know how to test. but thought since the rear switch works then the relay is fine?

I can't remember the D2 layout but it surely isn't the same relay for front and rear as you can put front fogs on without the rears.

Use a multi meter to see what you have at the switch. See if the live is switched properly by the switch.

I'd still start at the lamps themselves - could be as simple as both bulbs blown at the same time.

D2 Facelift has a 'control module' which is the size of 2 relays somewhere in the Passenger footwell relay box.

Its basically 2 latching relays that are driven by the two 'push to make' switches in the dash and drives the fog lights, front and rear. Theres not much to go wrong, but if its not bulbs or fuses, then changing the module would be my next option....

bulbs are ok, fuse is ok, no idea about the relay but since rear foglight works with that relay i think its fine. Don't really know how to check a relay properly.

A relay is a switch that is operated by another switch. The reason is that it will switch a lot more current than a small dash mounted switch can handle.

From IT's Post above it appears this Module is 2 relays in one item. There will be one feed but 2 load sides - one for Fronts and one for rears.

When the dash switch is operated a small current causes the relay to energise and connects the feed to the load side so if the relay is working you get 12 volts at both main terminals when it's on.

You need a mulit meter to check the relay as it gets switched. If you know nothing about electrics then I suggest you get someone who does as you could cause a lot of damage......

You say "bulbs and fuse OK" - how did you check them? :)

As noted above these symptoms point with very high certainty (if it's ALL fog lights) to a control unit/relay or fuse.


Fuses usually blow for a reason though......

Sometimes relays are standard units and there can be several identical ones in a car, facilitating "testing by swapping"; in this case though it's less likely due to the interlinked way foglights work with multiple inputs and multiple outputs.

Personally I would identify it and see if A8 parts have one available. Probably the cheapest method of initial diagnosis and quite likely a fix too.

i used a multimeter to check bulbs and fuse.
yesterday i did get the foglight on by accident. the multimeter pin connected to circuits when i was trying to measure the switch. So i don't really know what the problem is since both the switches works fine one rear foglight.

Like I said...

You were lucky that whatever you shorted caused the lights to come on, if you'd put the volts directly to earth it could have been serious :tuttut:

Best to get help :)