How to Wire the GMOS-01

by James T Wood
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The General Motors OnStar 01 module is designed to provide an interface between the OnStar system and an after-market stereo system so that all of the OnStar features are retained. The GMOS-01 comes with the wiring harnesses necessary to connect to the new stereo and the GM vehicle OnStar and radio systems. This installation should only be performed on GM cars with OnStar pre-installed from the factory, otherwise it may cause unexpected results in the vehicle's electrical system.

Step 1

Disconnect the negative battery cable from the battery before working on the electrical system in the car.

Step 2

Locate the 14-pin harness that came with the GMOS-01 unit. One end will have a plug with the other side having 14 wires with the last bit of insulation stripped from the end. This will be connected to the wires from your after-market stereo system. If it's not already done, strip the last half-inch of insulation from the wires on your radio.

Step 3

Twist the red wire from the 14-pin harness with the ignition-power wire for the radio. Touch the soldering iron to the bare metal of the connection until it's hot and then touch the solder to the wires until a drop or two melts off. Remove the solder and the iron. Connect all of the wires in this manner.

Step 4

Connect the orange-white wire from the 14-pin harness to the illumination wire on the radio. Connect the blue-white wire to the both the amp turn-on wire for the radio and the blue-white wire from the GMOS-01 module's 24-pin harness. Connect the brown wire from the 14-pin harness to the mute wire on the radio. Note, if the radio doesn't have a mute wire or a illumination wire, cover the bare wire with electrical tape. If the radio has a navigation system included, connect the green wire from the 14-pin harness to the parking brake wire, the blue-pink wire to the speed sensor wire and the green-purple wire to the reverse sensor.

Step 5

Wrap all the connections in electrical tape.

Step 6

Connect the yellow wire from the 24-pin harness to the 12-volt battery wire on the radio. Connect the black wire to the radio's ground wire. Connect the green wire to the left-rear speaker amplifier positive connection and the green-black wire to the negative. Connect the purple wire to the right-rear speaker amplifier positive connection and the purple-black wire to the negative. Tape the orange wire and orange-white wire separately to cover the bare wire.

Step 7

Cut the white, white-black, gray and gray-black wires mid-way between the 24-pin plug and the 12-pin plug. Strip the last half-inch of insulation from the wires. Connect the 24-pin side of the white wire to the left-front positive speaker wire and the 12-pin side of the white wire to the left-front positive speaker amplifier wire. Do the same for the other three wires connecting the white-black to the left-front negative, the gray to the right-front positive and the gray-black to the right-front negative. Cover all the soldered connections with electrical tape.

Step 8

Plug the 24-pin plug into the GM audio system and the 12-pin plug into the 12-pin port on the GMOS-01. Plug the 14-pin plug into the 14-pin port on the GMOS-01. Connect the remaining plug into the OnStar port in the vehicle's wiring system.

Step 9

Reconnect the negative battery terminal.

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