I agree with Rusty. Take out the taillight housings and clean up the rust around where the metal of the housing and the metal of the body meet. That is your ground. Use some small star washers on the screws when assembling.
I got 4 LED tail light's from farm & fleet mounted in 4 new metal hanger's every thing is new there is NO rust to Clean. . . this ain't no pickup truck guy. . . as for a ground truck's chassie has been stripped and repainted so I had go threw and reground every thing even used them shnazzy star washer's stainless bolt's and such. . .the singnal switch is more than likely the problem as it's 45+ year's old along with the badly rotten cab it's in. . .I'm hopping to have a new cab this summer so this should be the last summer i gotta cruze around in a rotten cab. . .But thank's for your in put guy!
Mike !
