Situation
You have a code for an open squib and when you clear the code, the light goes off, but comes back on with the same code a few seconds later.
Make sure the key is off, but the scan tool is still plugged in. Find the affected squib and unplug it. If it's the driver's squib, take it off from the clockspring. If it's in the seat, unplug it from the connector under the seat. If it's a seatbelt, pull off the pillar trim and unplug the seatbelt, etc. etc.
Get a jumper wire and connect the two cavities of the wiring harness together with it on the ECM side (don't short the component). Don't worry about blowing anything up, there's no voltage going through it. Don't be a scared little bitch. With the jumper wire in place, turn the ignition (not the engine) back on and look at the scan tool. Clear whatever codes are there and give it a couple seconds to run its self tests again.
If the code now says short instead of open, congratulations, you know you have a bad component. Write it up for the squib.
The reason why you know it's the component is because with the component out of the system and the connector pins shorted together, the ECM now can send voltage up through one wire, then have it redirected back into the ECM through the jumper wire and then the other wire in the harness. It reads this as a short, becuase there are no open circuits anywhere else in the wiring harness. Therefore, you know the only open circuit is in the component you bypassed.
If the code still says open then you know your problem is somewhere in the wiring harness. You'll basically have to repeat the process of jumping terminals with each connector, getting closer and closer to the airbag computer each time. Whenever the code switches to short, you know it's the section of wiring harness that you just unplugged. There may be more than one short in the system, but that's unlikely unless you have a rat problem or something. Either way, you're going to end up writing it up for the harness.