The COMPUSHIFT Sport and COMPUSHIFT Pro provide outputs to drive a relay for backup / reverse light and neutral start safety for most transmissions.
The exception to this is any of the 4 speed GM transmissions that use a pressure switch manifold for shift selector position like the GM 4L60E and GM 4L80E. This switch does not work unless the engine is running, and this defeats the purpose of a neutral start switch. For those transmissions, a separate external switch must be used for neutral start safety and backup lights.
HGM recommends automotive relays like Bosch PN 332209150. These are readily available at any parts store or catalog and are very reliable. A socket for them is also available for a tidy wiring job.
Instructions for the Neutral Start Relay
The neutral start output is a start inhibit. It turns on when the vehicle should not be started. Never connect this output to anything other than a relay.
The neutral start output is usually a white/brown wire that is connected to pin 19 of the COMPUSHIFT connector. Connect this wire to one side of the coil of your relay. Connect the other side of the coil to ground.
Wire the starter signal or starter relay circuit through the normally closed position of the relay and the common on the relay. In this way, when the relay is not energized, the car should start.
The COMPUSHIFT controller will turn on the relay in all of the forward and reverse gears, but turn the relay off in neutral and park.
Instructions for the Reverse Lamps Relay
The reverse relay output turns in when the shift selector is in the reverse position. The output does not provide sufficient current to drive lamps directly, and should never be connected to anything other than a relay.
The reverse output is usually a white/orange wire that is connected to pin 20 of the COMPUSHIFT connector. Connect this wire to one side of the coil of your relay. Connect the other side of the coil to ground.
Wire the backup lights to the normally open output of the relay, and connect the common side of the relay to +12V power through a fuse.
The COMPUSHIFT controller will turn on the relay in the reverse gear position on the shift selector.