GM Service Manual Online
For 1990-2009 cars only

Do not connect aftermarket accessories into the following circuits:

Caution: Refer to SIR Caution in the Preface section.

    â€¢ SIR circuits, all such circuits are indicated on circuit diagrams with the SIR symbol.
    â€¢ Always check for aftermarket accessories as the first step in diagnosing electrical conditions. If the vehicle is so equipped, disconnect the aftermarket system to verify that these add-on accessories are not the cause of the customer concern.

Possible causes of vehicle conditions related to aftermarket accessories include:

    â€¢ Power feeds connected to points other than the battery.
    â€¢ Antenna location.
    â€¢ Transceiver wiring located too close to vehicle electronic modules or wiring.
    â€¢ Poor shielding or poor connectors on antenna feed line.
    â€¢ Check for recent service bulletins detailing installation guidelines for aftermarket accessories.