Is this supposed to be hooked up to something?

 

That is a ballast resistor that is typically used on GM products. Mustangs have a resistor wire under the dash that serves the same function. They both cut the voltage going to the coil down to about 9vdc. If you still have resistor wire then you don't need that ballast resistor on the shock tower.

 

Thanks. I thought it might have been for the original I6.