Find the wire that supplies current to the ammeter from the battery cable connection at the starter. There should be a short section of fuse wire (fusible link) built into the connection. It's there to prevent damage to the rest of the wire harness when a dead short happens, such as the one you created by shorting out the wrench to ground. The simple way to find a burned fuse link is to pull on the wire near the starter terminal- - - -the insulation will stretch, indicating a burned wire inside. Replace the fuse link, and solder it into place. DO NOT use a crimp connector; it will create resistance and heat, and melt the link at the connection.
Forget the BS advice about bypassing the ammeter. Untold millions of vehicles have run their entire service life with functional ammeters, without burning themselves down or causing any problems at all. To have a completely adequate monitor of charging system performance, it would be necessary to have a voltmeter, an ammeter, and some sort of device to monitor the specific gravity of the battery acid, plus enough knowledge to interpret the results correctly.
Jerry
