Battery light when reving
 

when i rev pass 4000rpms my battery light comes on.......is this bad?

Yea your trucks a goner..























JK prolly pullin too much juice cause your battery is going bad, could be altenator, but i think it would then stay on. IMO

well its a new battery, and i only notice it lately when im reving high. but i think my battery has more cranking amp then the one i had before. prolly just producing more juice than i can use. when i get my brush guard and more lights it will use up more juice

Oh yea, be careful when i put subs and light in it ruined my old battery

thats why i got a new battery. sub and amp took the other one out.... i was splashing through tons of water on the road. maybe some got in there? everything worked totally fine

The brushes in your alternator are worn out. At high revs, they loose contact with the slip rings, and the output from the alternator stops. The brushes
are available separately, and aren't that hard to change.

Just guessing here, but..

overcharging = regulator
undercharging = brushes
normal voltage = excess diode ripple

I have to agree with Bob. The alternator is just worn out and can't handle the high RPM. Simple fix or just live with it.

Battery light at high rpm is s typical indication that the alternator is starting to go out. As Bob said; the brushes are probably worn.

Good morning...

Could let AutoZone do a (free?) charging system analysis with a pocket tester while alternator is still installed, just to be safe. Undercharging at high rpm will probably just evolve into eventually discharging at a lower and lower rpm and leave the truck stranded, especially with AC season coming up. Overcharging could be worse if voltage gets too high - I've seen fried ECMs because of bad regulators. If battery smells bad or looks like it's been boilimg over I'd guess overcharging. If not, I'd agree with just being worn out.

how bout starting the truck and disconnecting the battery wire if the truck shuts off you will know its the alternator

Absolutely NOT! You never want to disconnect a battery cable with the engine running. The di/dt can create huge voltage spikes that can destroy
expensive electronics, like the PCM, GEM, and even the alternator voltage regulator.

ive seen it done b4 with no issues but ur right i just came to mind