And of course the battery posts and clamps may need a good shine.
And, maybe ground straps connection points might need a good shine.
There are at least two ground cables/straps that attach to the frame.
And, since light fixture wiring did not include a ground wire for each bulb/fixture, the grounding was provided through the frame and sheet metal (and light/bulb housings). These "connections" might not be clean/rusted/uncorroded.
"ground continuity" is also affected by new paint in areas where sheet-metal parts and bulb-housings are screwed-on/attached.
You can test these ground by making grounding wires that have clips on the ends. Clip a wire to a clean ground-strap and to the lamp housing.
