[Excaliber]

My guess is that is a resistor for the ignition system IF you are using the old school point and condensor setup. Also used in some electronic applications, depending on the coil specs. Basically it drops the 12 volt primary voltage to 6 to 9 volts so you don't burn up the coil. SOME coils have an internal resistor, in which case you can hookup 12 volts direct to the coil, those without require an external resistor. Bottom line, 90% of coils require less than 12 volts or they will be damaged.

Not to be confused with the 400 volts an MSD box can suppy to a coil, thats a different animal, high volts but no amps to speak off, plus a special coil required.

I have such a resistor on my ERA firewall and have actually used it the few times I was experimenting with the old point style distributors. Which I could never get to work well beyond about 5,500 rpm.

They are usually ceramic body because they can get pretty hot depending on how it's used and for what. Like a heater fan speed control application for instance.