THANK YOU for drawing my attention to the importance of a good quality connection, but I am also a retired electrician and I know the dangers of a resistant connection that heats up and can, in extreme cases, cause a fire.
My photos could be misleading, I should have photographed the shunt alone without the ammeter.
For the final assembly of this shunt I successively placed on each stud:
- a brass washer,
- the shunt,
- a second brass washer,
- the cable lug that connects the battery on one side and the alternator on the other,
- a lock washer
- a nut tightened vigorously to exert strong pressure on the surfaces in contact.
I used iron wire because I only want to divert a fraction of the current so that the ammeter needle continues to deflect significantly. I tried with a single wire and there was still too much current flowing through the ammeter, with the two wires I think I found the right solution. If I wanted to get the same resistance with a copper connection, copper being about 6 times less resistant than iron I would have to use a copper wire of 0.1 mm (0.004'') diameter which would be much too fragile.
With a thicker copper wire, I would completely short-circuit the ammeter and what Panterapatt describes would happen, the needle would hardly deviate from zero.
I suppose that the ammeters installed after 74 with a copper shunt are much more sensitive than the previous ones and can measure a much lower current.