GM "R" Terminal Diode KitBallast Resistor BypassFor use with Breaker Point IgnitionsSold Individually JEGS 10038 R Terminal Diode Harness Kit is for use with GM vehicles originally equipped with breaker point ignition and ballast resistor. The wiring harnesses "R" circuit diode is a ballast resistor bypass. This terminal is "no connection" when the starter is at rest and provides +12VDC to the ignition coil during cranking for easier engine starting. Cars that do not have a ballast resistor (ie: HEI, MSD or other aftermarket ignition systems) should not need this connection. In most cases this wire will be eliminated, however, cars equipped with a ballast resistor (ie: Breaker Point or Mallory Unilite) may need this harness if the engine has no ignition during cranking, then the wiring of the coil is going to require an "R" terminal signal.