Because it just says 10amp might be some kind of breaker. Possible a broken reset button on the top. This is part of the problem with vehicles restored in SA. Not sure what what was all used. Since your is from SA and has a Aftermarket A/C installed is this part of that setup. If your 40 didn't have a heater you will be having to add the wiring for that.
Since your pulling the A/C and just adding the heater blower might be able to use part of that wiring for the heater. Would think long and hard before deciding to replace the wiring with something generic.
Probably should get a wiring diagram and see what it's tapped into, or ask the PO if possible.
It's kinda like a fusible link only resettable.
Caravaners use these for accessories like 12v electric jugs, outside lights etc. It may not even be needed. It could even be wired to the cig lighter socket.
Does it have a cig lighter socket?
These things are usually panel mounted. Is there a hole somewhere near it?
Because you have a SA import and the vehicle is over forty years old really going to be hard to tell exactly what it is. On these old cruisers just a general understanding of how electric works is a big help.