These quality heavy-duty relays are standard equipment on most British made race cars. The four terminal version (Part No. 1160-4) has an auxiliary switched contact (live while the starter is cranking). This can be used to bypass a series ignition resistor during starting on cars that have a resistor in-line with the ignition coil. Cars not using a resistor on the ignition coil can use the 3-terminal version (Part No. 1160-3).