battery light on. already replaced alternator and battery, fusible link shows continuity. mini fuse 20 amp is good 40 amp fuse is good ??????????

Could be a loose or corroded battery cable or other wire connecting components of the charging system,

If the battery light is on the alternator is not charging, it's not coming from the battery. possible you have a short somewhere in the car.

https://www.youtube.com/watch?v=9wLrTjeb9TY

Check the voltage at the battery engine running. It should be 14 volts plus or minus .5 volt. If it is around 14 the alternator is charging.

Thankyou Bob, I had already run all of the tests recommended. I replaced the battery out of frustration. 11.7 vdc at battery engine at idle. fusible link shows continuity. 40 amp cartridge fuse is good and the 20 amp mini fuse is also good. The alternator I purchased id rebuilt and Autozone has agreed to take it back and test it. if it is good I will have to find a good schematic diagram of the charging system. Chiltons?

Try here....http://www.justanswer.com/ford/1lu83-2000-f150-4x4- replaced-battery-alt-not-not-charging.html

If you are saying you are getting 11.7 volts at the battery while at idle, try this. Check the voltage with the engine off. Should be 12.5 volts. The alternator has to charge over battery voltage for the battery to charge. However, some electronic alternators will not charge at 14 volts if the battery is severely discharged. Also, the idiot light on the dash is controlled by the PCM. Someone with a live data reader can determine the problem rather quickly.