wired correctly, the stop lamps are always used for the turn because brighter - the signal mechanism "interrupts" the chosen lamp, letting the other light work with the brake pedal ... sounds like the gray is the feed from the stop switch, the black wire is the right stop/turn, and there's an existing wire to the left stop/turn .... you need to eliminate any cross connection already existing at the back between the 2 lights so they can act seperately
it may be a little hard to follow mentally, but draw it out, the stop switch supplies the signal mechanism, and R and L brake lights need to be seperately hooked to it so it can interrupt whichever is chosen, but let the other go by, or let both thru when no signaling done
Bill
