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The ABS front hubs have a cable that runs up from the hub behind the brake housing to the inner fender where it plugs into the ABS harness. Most times it is the hub-bearing bad that throws this code on 4x4 1999 F150. The bearings could be loose as well if this is not a 4x4. Take the truck and jack it up on the front end and take each front tire and wiggle top to bottom with the tire and see if the tires move in and out. If they do it is the bearings in the hub. Change hubs or bearings depending on which is on your truck. You can clean the ABS probe end that goes into the front hub as sometimes it gets dirty and that is all it needs. All or any of this will flip the ABS light on.
As the other poster said, you will need a scanner that reads ABS to see what code is being thrown and what side. Have seen where the cable has been broken out of the ABS system where it plugs into the ABS harness and you get a code for that as well.
Go to INNOVA.com best bang for the buck. Look for one that has the abs icon. I have the 5160RS FixAssist Pro
What ever you get make sure it is a scanner/reader NOT just a reader. Read about the ( RepairSolutions2) app it is the best feature for people with little trouble shooting skills. The more you pay the more features you get. Some like mine and others will cycle the abs pump for bleeding. I would download the operators manual before you buy no matter the brand or model that will let you know just what you can do with it.