I've been working on my 2003 3.0i. I just need the light reset so I can plug it in and see if it works:
I took some measurements and came up with the following:
161k Ohm - resistance with no occupant
8-11k Ohm - resistance with occupant, depending on seating position and weight
I rigged up a circuit with a switch to activate/deactivate the airbag. I'd like to add in a LED but it will require more testing to see if I can overcome the current draw. I used two 100k Ohm resistors in parallel to get a 50k Ohm resistance, in series with another 100k Ohm resistor and finally another 10k Ohm resistor ----> ground (output). Then in parallel I have the switch and a 10k Ohm resistor (should give me 9.4k Ohm of total resistance when closed, well within the occupant threshold). Testing revealed 158k Ohm (within the resistors' tolerances) when the switch was open and 9.4k Ohm when the switch was closed.
I really need a reset tool to finish up testing. If anyone is considering taking out their seats, disconnect the battery after you slide them forward and back to remove the bolts; otherwise, you'll end up with an airbag light. The DIY video I watched simply said keep your key out of the ignition. This is not the case.
With the M I plan on setting the resistance to the level where the "airbag off" light illuminates. I tried using different dumbbells to simulate the weight of a 25, 30, 35, 40, and 50 lb occupant (should deactivate the airbag and illuminate the light on the M) but no luck on the old 3.0i. It has a manual switch on the door, and there's no obnoxious beeping noise when an unbuckled passenger is sensed. Basically, I have no way of proving it works except that the resistance changes and no airbag light illuminates.