OK, this one is weird.  I'm guessing it's a short or something where all three positive leads are shorting with eachother, but, not sure...

If I use ANY of the three lights INDEPENDANTLY, everything works fine.  Blinker only, OK.  Brake only, OK.  Reverse only, OK.  There MAY be a little "bleedover" to another light, but not much.

As soon as there is ANY combination (brake + blinker, brake + reverse, reverse + blinker, or all three), then all three lights have current to them, and sometimes the brake/reverse lights blink with the blinker, etc...

Ummmm, how do I troubleshoot this?  Is it a short?  Fusepanel?

Look for a bad ground.  The power is feeding back through the ground system and lighting the light.  Clean the ground for those lights.

Definitely a bad ground. There should be a wire from the bumper to the chassis/body. A bad connection there is usually the problem.

I've checked the light assemblies, and they are good.  There shouldn't be a problem having multiple grounds from the assemblies to one point on the bumper, right?

Ground!!!

Bad Ground!

Take the tail-light assembly out and clean all the mounting points down to nice shiny metal. If the mounting screws are rusty - buff them up with a wire brush or replace them. If that doesn't solve the problem, run a jumper wire from the tail light housing to the frame or body. Be sure to clean the mounting point on the frame or frame down to bare metal.

David