Abstract: A lamp provides brake and turn signal functions for a towed vehicle while isolating the electrical lighting system of the towed vehicle from the electrical lighting system of a towing vehicle. The lamp includes a bulb, having an interior cavity, mounted to a bulb base. The bulb base is received in a lamp receptacle on the towed vehicle. The bulb base includes a positive contact region and a negative contact region. The positive and negative contact regions on the bulb base are connected to the electrical lighting system of the towed vehicle. At least one filament having a negative lead and a positive lead is located within the bulb cavity. The negative lead of the filament is connected to the negative contact region of the bulb base, while the positive lead of the filament is connected to both an isolator device and a lead wire. The isolator device is connected to the positive contact region on the bulb base, while the lead wire is connected to the electrical lighting system of the towing vehicle.