Hey guys, I used to sell turn signals on EBAY for this exact reason. Here's what you do:
Get a 12vdc piezo from Radio Shack ($4.00) and a 552 flasher relay from the car parts store.
Figure out which of the two pins on the flasher is positive, and which is negative, when it's plugged into the relay socket. You'll have to use a voltage meter, or know how to use a 12v lamp. Hot side to ground is positive. Remember, igintion on, and turn signal on, to find voltage

Then, cut wires to length, and solder the red piezo wire to the positive flasher terminal, and the black wire to the negative flasher terminal. Solder the wires right on the sides of the spades, up close to the flasher base. Don't overheat the terminal, or it'll ruin the flasher filament.
I usually used a little shrink-tubing to protect the wires routed along side of the flasher. Use some hot-melt glue to attach the piezo to the top of the flasher relay. It should look like a regular flasher, with a piezo on top. Nice and neat, and it'll fit into most tight spaces.
Plug the flasher into the socket, and try your signal. The ignition will need to be "on".
When the turn signal is engaged, the piezo will screech in between flasher pulses, until canceled. The voltage passes through the piezo while the flasher de-energizes, then the voltage flows straight through to the turn-signal lamps when the flasher energizes. Back and forth.
If it doesn't work, you got the red and black wires reversed. It's backwards on Chevy vs. Fords.
Also, this might not work if you've converted to LED tailights, because the load isn't sufficient. Same for a "Heavy Duty" flasher for trailer loads. Sometimes works, sometimes doesn't.
BTW: This works REALLY well for you Harley riders, too.
Hope that helps!
Ed Glenn (New Member)
1972 F-250