¿¿¿Weird Light Question???

[BadaSs_Cal]

First time drove the truck out of the yard today. I was worried because ( what I believed was a bad Blinker switch in the column) was messing with the brakes. If its in the Left blinker position only the Left break will go on with the break pressed in. And right position is only right break light.

So I just figured bad switch, or my wiring is screwed up.

Well then it got dark, so I tried my luck with the markers and they work fine. And so does everything else. The blinkers, brakes, everything functions like normal.

So what the heck?

What would make that happen?

Im using those universal 2 wire lights round lights you see on everything from old stepsides, and trailers.

[old cruiser]

My first check is always the ground wires the ground or earth wire depending on where you're from is normally the biggest cause of electrical issues

[61_FL_Apache]

Check the ground on the tail lights.