The diagnostic monitor plugs hold an electrical charge in case the battery is damaged during a collision and allows the air bag to deploy even if battery is disconnected. During a rescue situation we will cut the battery cable then attempt to discharge the air bag so as not to deploy (if applicable). A side impact would neccesitate this type of action.
You found the problem!
First, I want to point out that to others, that when you said
to hook the Battery back up while
You meant connecting the main car battery. Not a "backup battery".
Also, you were likely reading a brief procedure for just that error. Before doing ANY air bag system test, a Service person should:
1) Disconnect the battery
2) Wait 1-5 mins
3) Disconnect the air bag(s)
4) Put in air bag simulators
5) Connect the car battery
6) Do tests.
You can "back probe" the air bag connector pins. Or, there are DVM probes that have *very thin and sharp* probe ends. One of those probes ends are then used to pierce through the wire insulation so that the wire can be probed. Those probe ends are so thin, that when they are removed, no hole is left in the wire insulation. I forget the cost of a pair of those probe leads. My "wild *ss" guess is ~$50. Yup, I have a pair from over 15 years ago.
Back to the code 12 error. Yea, it's one of those errors that should never really come up. Many months ago, another person and I spent a while tracking down the problem. It ended up being a bad diagnostic module. The modules are cheap. Just get one fron car-parts.com just about every place will ship, and it's one of those things that often makes sense to buy used.
I'm glad that you found the problem!
That's for sure! When they designed the Fox interior, there weren't air bags to worry about. Air bags weren't added until 89. So, it was a squeeze to add in the airbags. Like everything else with the Stang, to keep costs in-line and profits higher, Ford avoided doing any major changes.
So, I take it no more error 12?
Opps, you're right.