You note that your speedo drive was unhooked behind the dash. It is entirely possible that the speedo cable, while spinning, took off the insulation to your wiring and caued a dead short to the transmission or firewall. Ask me how I know. I let the smoke out of the pink wire behind the dash of my '61 in exactly that way. Perhaps a re-look at the proximity of the speedo cable to the affected area on the wire might show this to be possible in your situation. And then you might rule out the gauge and simply rewire again as the factory did. Inline fuse on starter circuit=bad idea
