Take the white wire away from the OEM signal switch, add about 25 feet of white wire to it, and route it to all 3 brake lamps. The 2 wires that carry stop and turn current to the OEM rear fixtures can be taken from the OEM lamps and rerouted to the addon amber turn fixtures at the back of the vehicle. You could change the OEM rear bulb sockets to have same 1156/single filament bulb type in all rear lamps.