![Image](https://i.ibb.co/7WdXpDj/20220618-181150.jpg)
It is very simple. The battery side has a flat plate a bolt head screws down into. The output side a 10mm long thread the bolt goes into. The halves of the device separated by an insulator.
Mine failed. Turn on ignition - fine. Go to use the starter and nothing - dash lights etc go out and stay out. Undo the bolt and redo - works fine until the next time.
So gave it a good clean with a wire brush. Bolt is brass and comes up like new. Plate the bolt head clamps onto clean too. Which only leaves the thread the bolt goes into.
Noticed the body isn't made of brass, but some metal which doesn't rust and plated to look like brass.
Could it be that plating is acting as an insulator after a few years use?