Thanks for sharing this photo.  Excellent example.  Looks like an easy fix.

Troubleshooting techniques save paying n.
When power isn't going to where it should, go to where it originates.
If it's there
Go half way to where it's supposed to go, in this case, tail lights.
If it's there
Go half we closer.
If not, go half way towards the origin.
Air Force tech school.

It Can be put into a coma, though.
Ospho, a dilute phosphoric acid, available from Kelly Moore paint stores, turns iron oxide into iron phosphate.
Preparation is key. It only affects the surface. So, if you can't see the metal through the rust, it's just gonna come back.
Absolutely NOT to be used on blued metal. Unless you're wanting to reblue it.
Only works on ferrous metal.
Don't buy the gel. It sux.
I've kept a bottle in the shop for over ten years. Handy for little places you don't have time to do right, but you don't want to just let it grow.