jeeprizm

I have a 2002 Prizm LSI that is one of the best cars that I have ever owned. But recently ( last week) when ever I turn my left turn signal on and push the brake, the signal flashes fast like its burnt out. But when I walk to the back of the car I see the brake light flashing brightly and fast, the side marker light, turn light, and both reverse lights flashing fast but dimmly. I took the left back tail light apart and found nothing wrong with the sockets or wiring,no nicks, freyed wires and all bulbs are fine. I did replace the rear break light bulb on the left a couple months ago but every has been working fine.The front left signal light works just fine but that flashes fast when I push the break but it doesn't dim out. It seems like I have something grounding out but I don't know where. I figured you guys could help me out in a bind like this.

Any help would be greatly appreaciated,Thank You

Jeeprizm