Most commonly the flasher - usually located in or near the fuse box - perhaps at the left lower side of the dash by the steering column it just plugs in
Check fuse and turn signal flasher relay.
How do you remove and replace the battery on a 2001 Ford F150?
location of flasher relay ford 150 2004
Replace the Flasher Relay. Located Front seating area, driver side, behind left hand side of instrument panel, on fuse panel.
On a 2001 Ford F150, the turn signal flasher is located in a relay box on the passenger's side of the steering column. To access it, you must remove the panel under the steering column.
most likely would be a bad turn signal flasher
Chainsaw
how to install alternator2001ford f150
How do you replace the tail gate latch on a Ford f150
change the turn signal flasher flasher could be a fuse
take off the distributor cap see what you find.
I had to replace mine after it broke. All I did was remove the OLD stub with a crescent wrench and replace it. It took about 1 minute. That is all you have to do.