Technical How to ground 63 ranchero tail lights

I'm running new wiring and I just for the life of me can not figure out where to ground the old tailights with my new harness

 

Just ground it to one of the mounting screws of the housing...

 

My non-Ranchero Falcon taillights are grounded to the trunk floor with sheet metal screws.

 

What I'm asking is do you just run aground wire from the housing to the body oristhere anouther wire on the tail light that should be a ground. I only have two wires by the way

 

There should be a connector tab on the bucket for the ground wire. I think there is a factory sub-harness that grounds both tail lights and the fuel filler neck.