'03 SCrew, 5.4, auto, 4x4
Yesterday my left turn signal started flashing fast; checked and the front was not flashing. Picked up a new bulb, changed it, didn't fix anything.

I've tried:
-tilt wheel up/down in all settings-no change
-checked the wiring at the top of the column; still good and solid (thanks to information I received here before).
-swapped the bulbs left to right and vice versa-no change.
-swapped the sockets left to right and vice versa-no change.

Other info:
-the left front is the only one not flashing with hazards on.
-all original equipment, except I removed the stock side mirrors (w/signal) and installed manual trailer towing mirrors, but that was 2 or 3 years ago.
-the dash indicator light for left turn (arrow) does not come on at all.
-last trailer tow was over a month ago and all was good.

I ran out of daylight last night and at work now so I would like to get some help as to which Fuse, Flasher, Relay, etc., I should check/replace and where to find them on the truck; under the hood (1st or 2nd stack of the fuse blocks); under the dash above the pedals; steering column???

Thanks in advance,
Brent