[hplacecf]

made some progress.
thanks for the help.

definitely was/is a ground issue, but still not working 100%.

So, based upon the advice I received here (thanks again!) I attached a ground strap:

from the bolt that sticks out from the bed on the driver side at the rear bottom (and appears to be used for a bed ground wire used for the lights on the driver side of the bed)
to the frame.

Once I did that, I instantly had taillights on again. Even when I moved the bed around (bed bolts are on, but not tightened down yet).

To double check, I disconnected one end of the ground strap and I immediately lost the tail lights until I moved the bed around - so this proved that the ground strap was helping.
I attached the strap and had tail lights again wherever the bed was moved around to - good so far.


But, my issue now is this:

if I put on the 4 way flashers with the lights on,
the passenger side flashes between low light (as it should with lights on) to bright light (as it should with a blinker or 4 ways flashers) - so the passenger side is good.

but,
the driver side tail light goes dark - no low light for taillight, and no bright light for flashing - in time with the passenger side light.
same thing happens if I put on the passenger blinker.

If I put on the driver blinker, the driver blinker does blink, but it goes from all dark to low light (tail light on brightness) - no bright blinker light.

Do I need multiple grounds?