Time to update this thread and ask some more questions..
Further to my tail lamp issue, I figured out why the upper marker lamps would not work when I put the LED's in
They are made by Grote...
Her is a view of the internals... complete with incandecent bulbs.
I already mounted the rear ones, and if you notice the Ground connection is handled by the tab under the mounting screw...
The Incandecents worked great, but when I swapped in the the LED bulbs, they would not work.. so I swapped the incandecents back in.
Now I have the front markers on the bench and wanted to figure it out.
Connected the body to a ground, and the wire to +.
The Incandecents worked fine.
Put in an LED, on one side... Nada... Nothing, but Incandecent was working fine.
Now, I know that LED's are polarity sensative, so I swapped the connection... Body of lamp + and wire ground..
Now, I looked closely at the fixture..
Note... the gold colored metal is connected to the single wire... so should be +... yet its the body of the bulb...
And the silver colored metal that has the the screw tab... that would be ground is connected to the center post of the bulb...
What is up with that?
I always thought the center pin is + and the body is grounded....