Maybe this is normal, but anytime my rpm's reach about 3 grand my battery light comes on, and stays on until i drop back below about 2800 rpm's. Is this bad, and what is going on!
Thanks for any info

 

by the way, this truck is a 98 4x4 with 4.6 and auto trans.

 

Its not normal but I don't think it is terminal. Poss the belt is losing traction at the higher RPM and allowing the alt. to slow down. Only thing I can thing of off the top of my head..

 

Your voltage regulator may be gone allowing more voltage than you need to the battery at high RPMs. Put a voltmeter across the battery teminals. It should read between 13 - 14.5 volts at idle. Rev the engine and see if the voltage stays in that range. If not, then you are cooking your battery and the regulator (part of the alternator) needs replacing.

 

From the 1999 + using the DTM on the HEC, the Battery range shows :
8.5-10.7 volts, Normal band start
15.8-18 volts, Norm band end

If the battery is above or below this level, it will illuminate the battery icon on the dash.

Easy test, hook a set of wires to the battery and run it through the hood in an area that won't pinch it, and through the pass windiw, and use a volt meter to get a reading on what range it happening while driving both above and below the RPM range.

If it is under, first check the belt for slippage ( should hear this inside the cab ).
If it is over, regulator I would guess, but either way have the alternator checked.

Good luck