[PxTx]

Sounds like you've got a dead short if there is a click just before the fuse blows. It has been a while since I've been through the wiring in these old cars. Is the cig lighter on the same circuit as the radio?

I would install the radio fuse and then grab a multi-meter. Put one lead on the negative batt terminal and start checking your leads on the turn signal circuit. Repeat on the radio circuit if nessisary.

You'll be looking for stray voltage. Ideally you'll have 12 volts on the positive terminals and 0 volts on the grounds. If there is less than 12 votls on a positive circuit or more than 0 volts on your grounds then I would look more closely in that direction.

Since it blows the fuse repeatedly you are actually in a good position. Figure with the radio fuse out, one of the power leads is just and open wire, fuse-in is providing power to the shorted area. The short is occuring when there is power being supplied to your turn signal ground(s) I suspect. Now that I type that, I'm thinking it's the other way around with the turn signal power shorting over on a radio ground, since it is the amps on the positive side which is blowing the fuse.

Again, I'm unclear in the specifics of these old harnesses. Can anyone else clarify things better? Am I going in the wrong direction?