No. Make certain you are on the ammeter terminals and not something else. ammeter SHOULD NOT have sheet metal nuts
On a side not, PART OF the danger of ammeter failures is "the sandwich." This varies as to year, IE, my old 70RR had a plastic housing through which the ammeter studs passed and when things loosened up, got warm, the plastic got soft, things got looser. ==The "snowball" effect, or if you prefer, the "fireball" effect.
If you can, tear the ammeter apart, clean the studs and shut and solder them. Best if you can silver braze them, but solder will do, get a good connection. Then examine the "sandwich" that is, the stud, sandwiched to the shunt, sandwiched to whatever else in there, the insulating washers, etc, and out the back where there should be two hex nuts to tighten it all. Star washers won't hurt, and neither would a couple of well fit flat washers on the bottom to distribute pressure. Then slip on your red/ black and use hex nuts on those too
I don't remember how you tell which is red and black, I think some are marked. The worst that will happen is that it will read bass-ackwards and you'll have to swap the two wires