I just done mine quickly and tbh its not the best way but, i spliced the live wire that goes to the front fog light switch, and ran the wire down to the OSR cluster, put a capless red LED bulb in the bulbholder, powered it with that wire and earthed it on the light securing bolt. Hope that makes sense lol. Only downside is that once the fog light switch is pressed then all the fogs are on but it doesn't bother me. And use a good red LED, i bought one for a quid and its not that bright. Rear fog is supposed to be brighter than brakes for MOT and obv for when its foggy.