I don't see a "strap" that you call ground.
I don't know why the old ammeter has three posts.
What thing has the words IN and OUT? Who marked it? You or the conversion person? Who converted it?
If the box is a resistor, it would not have IN and OUT because a resistor is not polarized. If it is a circuit breaker/fuse it could be polarized. A person with electrical knowledge would not use the words IN and OUT. It's pretty much meaningless and open for error/misinterpretatio when wiring the back of a converted ammeter. Probably was cleared up in the lost instructions.
Last edited by bartamos; 01/21/2025 9:29 PM. Reason: added thoughts