I have a '98 Tacoma that periodically likes to light up the left turn lamp (front and back) when I apply the brakes. This has the added effect of cancelling the blinker on that side. I looked at the reflection in a storefront when this happens and the turn lamp lights, just no longer blinks. And the kicker is that it doesn't always do this - just on days when there are more cops nearby!!!! I have an aftermarket module for my trailer lights and kinda suspect its electronics, but is there something else that might be doing it?

Disconnect the trailer module first and see if the problem is still there. Have you checked for water inside the signal lights? Wet connectors can cause some strange problems.

Clifton