[cgtech]

First, no frame grounds right? Do you have any 12v metal switches or parts touching the steering column or brake pedal? Do you have turn signals or brake lights, or only running lights? Trying to identify any ground. Also look for any of the small light system wires running parallel to the large high current cables, possible induced current. Try putting a standard brake lamp bulb on one side only, then observe what happens with both taillights.