…it’s not hard to fix. An ammeter will stop working for several reasons, a common one being that one or both of its two wires are broken, frequently within the wire harness sheath where it can’t be seen. To get it to work again, try running two new wires to it as follows:
1. Get about 10 feet or so of 16 gauge wire and, if you don’t already have this stuff, a box of assorted crimp-type connectors and a combination wire cutter, stripper and crimping tool;
2. Run one 16 gauge wire from the large terminal on the starter solenoid (to which is connected the positive battery cable) to the ammeter. Route this wire up to the firewall, then across the firewall, preferably behind the large wiring harness that runs horizontally low on the firewall, then up alongside the harness which leads to the large rubber grommet high on the driver’s side of the firewall. Push it through one of the holes in this large grommet to the area behind the dashboard and connect it to the positive terminal on the back of the ammeter;
3. Run a second 16 gauge wire from the BAT terminal on the voltage regulator, down along the wires from the regulator, then across the frame alongside the first wire, to the negative terminal of the ammeter.
The ammeter should now work. If it shows discharge when it should show charge and vice versa, reverse the 2 wires at the back of the ammeter. If the ammeter does not work at all with the new wires, it may be defective and in need of replacing. Make sure you buy a ’49 ammeter and not a similar-looking ’50. Also, it is important that the wires be no larger than 16 gauge as the ’49 ammeter is wired as part of a shunt system, which means only a small portion of the car’s electricity, 1 ampere or so, goes through the ammeter, unlike ’50 Cadillacs through whose ammeters all the electricity flows.