I understand that well, Kevin. Thanks for mentioning the parallel resistor scheme, however. I've discussed that on this forum, but I get the idea it isn't in everyone's comfort zone. What I meant to say was that a shunt might help somewhat, but given the design of this ammeter and the internal shunts (there are actually 2), the numbers don't make adding a third (or a second if you want to look at the ammeter as a primary shunted device) that easy. And the thing is any ammeter must be (or remain) linear in delivery and I'm not convinced this one ever was all that linear.
Small correction, but the shunts in this case are only reducing the current flow through the ammeter itself. They form sort of a freeway of current that is intersected by a small sidewalk that is the ammeter itself.
You can see the shunt design below. First is the brass framework cage (goes from post to post continuously) and second is the 1/16 thick piece of steel joined to the top (right beneath the gauge face). Which as I said possibly could be seen as one shunt device. The resistance of the OEM gauge is .003, so with 50 amperes we have about 1.5mA current flowing through the meter and we probably need something like 2mA with 100 amperes. At least that would match most of the internally shunted 100 amp ammeters I've seen.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
