Hot ammeter

Read this article:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml
In the meantime, unhook the battery, get up under the dash and unbolt the large black and large red wires from the ammeter, and bolt them together with a screw and nut and tape off safely. The black IS NOT ground. The red comes fromt he battery, the black feeds off to loads, and goes back through the bulkhead to the alternator output stud