Left front blinker not working/blinking fast in left rear blinker

check other turn signal bulbs on the same side of car. If there ws a fuse problem he flashers would not work Fuses only protect wirreing and do not cause problems

You obviously have a bad connection somewhere in the taillight. Some trucks it is a common problem and the taillight circuit board is the problem.

Check the switch

When its blinking fast look at both front and rear to verify which bulb isnt flashing. If the right works OK, then the flasher is OK. The flasher is INSIDE the front control module/integrated power module. If you cant find the problem, you may need a dealer to check it.

When a turn signal bulb is blinking fast, it is an indicator that a bulb is bad in the system. Replace the left rear turn signal bulb, then see if the left front blinker has gone back to normal. This is most likely your problem. Let me know if it is still a problem and i will help you fix it. Good luck

Sounds like wrong bulbs in some sockets

the fuse is broke

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

Usually a fast turn signal means that there is a light out. You should probably check all of your lights, including back-up lights, and turn signals. If there is one out then replacing the burnt out bulb should fix the problem.

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.