ok, this is the main ign live feed for the coil, if this is really dropping to 9v then that would explain everything! for a test, run a fused feed from the battery direct to the spare spade on the coil, on the side where all the other black wires are. take it for a few runs, if problem gone then i would replace the ignition switch.
you'll need to disconnect this wire from the battery before the car will turn off
