97 Ford F150 4.2L Battery will not stay charged?

Pretty much 100% sure it's your alternator.

http://www.carbasics.co.uk/How_to_test_your_altern...

That page will show you how to properly test it.

You surely have a problem. You have short some where check alternator, starter solenoid,and check any and all wires that run thru fender wells and up front to your head lights and under the truck towards the back. Some times the wires get rubbed bare and you cant see it so just reach and grab them where the go thru some metal and give them a little shake.Some times that will dislodge the shorted wire.When all else fails take it to a mechanic shop that specializes in electrical such as a starter ,alternator, or battery shop. Hope this some help. Good luck and god bless.

a good aspects keep could additionally try your starter for unfastened. an hardship-free thank you to work out in case you have something drawing ability from the battery is : do away with the helpful battery cable from the battery. Clip a 12 volt try easy to the helpful battery terminal & positioned the different end of the try easy on the helpful cable.If it lighting fixtures fixtures up with the biggest interior the off place,you have something drawing on the battery.if so start up pulling the fuses one at ta time,til the lite is going out,that'll be the subject.

Alternator which Ford trucks are known for going bad as well as electrical problems

Check the alternator , it could be shorted out and draining your battery .