Electrical Gremlins
Troubleshooting electrical problems in old cars can be a challenge sometimes. When a component fails, like a light bulb, it's relatively easy to track down and repair. Other faults, like corrosive resistance at a connection, an open circuit, or short circuit to ground somewhere can take time.
The '63 T-Bird came in with a couple of blown fuses and no dash illumination or working turn signals. Someone had cut off connectors inside the doors for the courtesy lights and we even discovered a ground wire for the headlights connected to power at the starter relay. So, there were some weird things.
While the dash was apart, we replaced fuses and everything tested okay and worked fine. But as soon as things were fully reassembled, the fuse for the turn signals blew again.
Somewhere between the fuse panel and the turn signal switch we had a direct short to ground. We disconnected the turn signal switch from the harness to rule out anything going on inside the steering column. A test light at the fuse panel indicated there was still a short.
Power travels from the fuse panel to and through the turn signal flasher and then on to the switch. The flasher is inconveniently clipped into the back of one of the gauge pods, so the pod was removed (again) for access.
Once the flasher was unclipped from the pod, the test light went out - the short was gone. It turns out, even though the flasher worked, power inside was being short circuited to the metal case. As soon as the unit was clipped into place on the back of the dash it was grounded to the chassis which, in turn, blew the fuse - as it should. All it took was a new flasher from the parts store. and the gremlin was eliminated.