chances are it's the voltage regulatorit could also be a wire no connected on the alternator
Weak battery or alternator output.
Possible causes,- Faulty battery- Alternator belt missing or loose- Faulty Alternator- Alternator harness is open or shorted- Alternator circuit poor electrical connection
either the alternator or the voltage regulator are no good.may also be a bad battery
Defective alternator or internal voltage regulator is bad.
Your battery is weak, or your your alternator is not charging battery.
Failed battery, or alternator is overcharging.
poss alternator fault
Can be loose or corroded battery connections, loose drive belt, or the alternator is failing.
Alternator is defective and needs replacing.
It's not charging the battery. Check the alternator.
could be a bad battery
your alternator was never the problem. Its your battery and/or charging system. the reason the lights get brighter is because the car isn't getting the propper amount of energy from the battery and is having to directly draw off of the alternator. when the engine is rev'ed the alternator spins faster creating more current to charge the battery, witch is why the lights brighten at higher rpms.