Brake light, taillight, turn signal issues.

We recently bought a 2003 Tacoma. We believe at some point, it was either flooded of driven into a deep pool of mud/water. When the rear lights are used individually, everything is fine. However, hit the turn signal, then the brakes to slow down for the turn, both the turn signal and brake lights on both sides including the brake light on the cab begin to flash. This also happens when the taillights are on. It seems something got wet maybe? Has anyone ever experienced this kind of issue? I really don't know where to start.

 

Do you have a trailer tow harness? If so, remove that first, they tend to fail and start causing issues like this.

If that's not the case, you will need a multimeter and some time to trace the circuits. Turn signal and brake lights come together at the tail light bulbs, I would start there.