An intermittent SIR light in my 99 Blazer was difficult to find and correct. The manufacturer's code indicated it was a fault in the "loop". This turns out to be something in the wiring and crash sensors (which GM calls the "discriminating sensors"). These should not be confused with the clock spring, which also physically looks like a loop. It was a $200 lesson for me to figure out this was not the "loop" in the diagnostic code message. The crash sensors list at about $400 each, though they can be cheaper on eBay. The problem turned out to be the drivers side sensor. The sensors are roughly an inch and a half cube and are located under the radiator. The two are wired in a series/parallel "loop", with the right side at the end of the "loop". It terminates with a 1000 ohm resistor, allowing the controller to monitor continuity. I was able to determine it was the drivers side sensor by shorting the two yellow wires together and the two black wires together in the connector for this sensor. This bypasses the sensor and caused the intermittent light to go away. The sensors were riveted in place and had to be removed with a nail pry bar. Always wait at least 15 minutes after disconnecting power to the air bag before dealing with the wiring so that you don't inadvertently deploy the air bags. The controller stores enough electrical charge to deploy the air bags even if their power gets cut during a crash. It takes that much time to be sure that charge is depleted.