I take it that your starter motor is a inertia type, according to my P6 Manual, there are only two small wires to the solenoid. white/red to actuate it from the switch and a brown to the voltage control box , but I would expect that to be a 3/8" wide Lucar. The brown goes to the same terminal as the battery cable. If you look in the manual you can see which wires go where. What year is your vehicle to help identify the circuit ?