First off, I have a 99 F150 XLT 4.6 5 speed.

Ok so driving home last night, my voltage is gone. I stop at advance and the battery is kaput. I buy a new battery, have them put it in. Well, battery light is still on, but I don't think it's the alt because I was still moving fine even with my battery being all but dead. It's mainly whenever there is a load on it when I notice the voltage drop and the battery light is full on, and when I'm at idle/clutch in, the battery light just flickers. I also noticed when I roll my windows down my voltage drops BIG time. And I also never noticed this before, but when I start the truck, all my guages go all the way up, all the way down, then to the spots they are supposed to be. Anyone have any ideas what my problem may be?

 

When I had my 01 F150, the gauges would sweep when the battery was dying. But you just replaced it so I wouldn't know what to tell you other than go back to where you bought and have them test the new battery - just in case. Then go from there.

 

your alt is shot , the battery was only discharged, you waisted money by not trouble shooting the system, if they or you had a multi meter you can turn the headlights on and check voltage, about 14 with a load on and you are good

 

Well had the alt tested and the regulator was gone. I went ahead and bought a whole new alt because they had them in stock compared to waiting 4 days for a regulator, and the regulator has a 90 day warranty compared to the lifetime on the alt.

And for the battery it was worth getting a new one anyways because the one that was in it was too small, it was for a damn honda.