E30 Zone

Hi everyone,when i turn on my lights my rear fog light comes on and i cannot turn it off at the switch,i have change the switch for a new one but it still stays on,the fronts work fine,any help would be appreciated,thank you.

Has this started after you did anything else on the car, taken off the rear light cluster or anything else?

yes,i did to change a bulb but not fog light.

Relays K4, K8 and fuse 15 all need to be good for the rear fog lamps to light in the intended way, but when the switch is off, they should be off.
You say you've changed the switch (simply unplugging it would have been better), so it looks like the lights are being powered by some source other than they should be.
This could be a short circuit to another lighting wire anywhere in the loom, but the fact that you've changed a bulb at the same time as the fault started is rather suspicious, so start your search in that area.
I take it both rear fogs are on, so start by unplugging the cluster that you changed the bulb on, and see if the other fog now behaves.
Similar faults are often caused on other vehicles by someone fitting a single filament bulb in place of a twin filament one (the single, central connection on the bulb shorts both contacts together), but this does not apply to E30s, since no twin filament bulbs are used.