On February 27, 2024, I had half an hour available to dissect the failed "Lucas" branded battery cut-off switch. Drill out two eyelet rivets and remove one small E-ring in back to separate the housing. Inside you see the large copper (or brass) contact plate that rotates to make connections on the studs in the lower housing. It looks simple enough. Separate the moving parts from the front housing. From back to front we have the brass contact plate, a steel cup washer for nesting the large diameter coil of a conical coil spring, then the spring, followed by a brass detent plate, which provides the click stops at both extremes of rotational travel. Physically it works fine, but electrically it had no contact.

The culprit here (I think) is the conical coil spring, which can be easily depressed with a simple pinch of your thumb. Apparently there is not enough spring force to make a reliable electrical connection to carry up to 200 amps current to crank a starter motor. In fact the final failure condition didn't even make a connection good enough to run the fuel pump or ignition coil, no electrical connection at all, even with repeated mechanical switching on and off. Maybe the contact plate was stuck on the square shaft so it could not be pushed down by the spring. Or, maybe plastic in the lower housing between the power studs was touching the contact plate to hold it up as not to touch one of the power studs. In any case, 100% electrical failure of every switch I've had in my car in the recent years is enough to recommend to the world at large not to buy these junk reproduction switches, guaranteed to fail.