I have a 1994 gmc sierra and when i turn my left blinker on the front lights blink really fast along with the arrow on my dash but the tail light wont blink at all. Also my left tail light won't turn on when i press on the brakes but my running lights work.

Your problem is either a bad bulb in the tail light/brake lights or your turn signal switch is bad. I'm more inclined to say that the problem is the turn signal switch and you need to replace it.

There may be a short in the front socket. Remove the bulb and inspect the socket for damage. If corroded, clean it up or replace it.

check earth wires for light circuits and dash

Your right rear turn signal bulb is blown.Replace the bulb and the fast blinking will stop.

the fuse is broke

yep bad ground in the dash

any increase in bink speed is direcly related to a bulb being burt out.

Blinker too fast, the same side blinker light bulb on the front (or back) is burned. Check the fuses for the rear lights. You might have a light bulb filament stuck.

Most likely it is a groung issue where your rear wiring harness grounds to the frame. There may also be additional grounds for the wiring harness along the frame before the ground by the rear bumper. One other option is to make sure you have the correct bulbs in. I have seen something pretty similar to that caused by improper bulbs. Make sure your bulbs for the brake light/turn signal have dual filaments as that could be an indication you have the wrong ones; if you have the bulbs I think you do.

Look up under dash where brake pedal pivots, you should see a switch that is activated by pedal arm.