Your "Old Timer" is correct about the Ignition switch, I wouldn't pull power from there. On my '46, the turn signal power was tapped off the headlight power input. If you follow the wire from your ammeter to the headlight switch, you will see two additional screws for tapping power at that terminal. As stated previously, you can tap power at either side of your ammeter. Either of these connections will give you unswitched power to the turn signals, I personally don't see that as a problem as a flashing turn signal is quite easy to notice from inside or outside the vehicle.
If you wanted switched power to the signals I would suggest using a standard 30 amp relay triggered by the ignition switch to power the circuit. You could get a larger relay and a small add on fuse block and use that combo to power the radio and heater fan also.
Steve
