I had my battery die on me this week and tested it at my work which indicated a bad cell so i replaced the battery. However, within the last 2 months I've noticed my voltage on my scan gauge will drop to 12 volts with the headlights and AC on, but ONLY when in drive or reverse gears. I've already changed my alternator this afternoon but still the same results. I've already checked my connections and battery terminals for corrosions. What am I missing? All of my top techs at work hinted at the alternator even though I had it rebuilt in May of this year.

 

Charge up the battery, then start the truck. Pull off one of the main battery connections. If it dies.... the alternator/voltage regulator is bad. Of course, make sure all of your fuses/relays are in good working order.. Kev

 

Found my answer... The wire going from the fuseblock to the conduit had corrosion therefore high resistance. I ordered a wireloom from my buddy at a Toy dealership.