I replaced my battery less than a year ago and checked the connections. the light still keeps coming on aand off. So I'm guessing the alternator is the next thing to check. How do I tell if its the battery or alternator?

 

The easy way to check is while the truck is running pull the red cable ( positive ) if it dies its most likely the alternator if it doesnt the battery is bad.

 

NEVER disconnect the battery with the engine running. It can ruin the alternator, PCM, and other expen$ive electronics.

Read this thread:
https://www.f150online.com/forums/el...ery-light.html

Using a cheap digital multimeter, check battery voltage with the key off, and again with the engine running.

 

It was the alternator. Was only pushing out 11.6 swapped it with one from an expedition and truck is good to go. Also replaced the belt. Took forever to get it put on right