Is this a ballast resistor?

[DanMcG]

And more importantly, I'm actually looking for the mounting location on my 85. Does it go on the top of the inner fender or the fender? It doesn't line up with any of the existing holes, but the fender is an 84 and inner fender is aftermarket. thanks

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[75gmck25]

Ballast resistor is only used with points ignition, so it would not be on a ‘78 or an ‘85 that have HEI.

AFAIK, that type of resistor was used to change the setting on an aftermarket trailer brake controller. Changing the resistance (loosen thumb screw and move the slider) changes the voltage applied to the trailer brakes when you press on your brake pedal.

It’s not OEM, and there is no need to reinstall it. Modern brake controllers work much better.