When i'm driving in the night, the intensity of interior light vary. My alternator charging at 75 amps full load, 13.6 volts. Is't a problem with the alternator ?



Thanks for your answer

What car, what lights? Are you speaking of the dash lights or the dome light? If you suspect an alternator problem you can take it to a number of different national auto parts stores and most will test it for free. Are the lights flickering, do they get bright and stay bright, when does this happen? Does your car have auto headlights that turn on when it's dark?

It's a Malibu 2004 LS (New style) with automatic headlight. The accessory light in the car vary in intensity.

OK, that's a lot more info. I can guess that by the accessory lights you mean the dash lights.

I know this sounds simplistic, but first check the dimmer adjustment for the dash lights. On the '08 and up it's a small knob on the left of the dash panel. If yours has a multi-function switch (MFS), meaning that the headlights are turned on manually using the end of the turn signal stalk, then you'll have the same or similar. If it's adjusted near the lowest setting then the lights could be fluctuating between very dim and slightly brighter. It would simply take adjusting it just a little brighter to fix it.

Next thing to do is to determine when they are varying in intensity. You can have the headlights on during the daytime by either turning them on manually with the MFS or by using the wipers continually. If you have the lights on in the daytime and the dashlights are very bright but become dimmer when it becomes dark outside (determined by the ambient light sensor) then that is normal. The '08 and up models do this so that you can see the instruments clearly in the daytime, but when it's dark enough outside the system dims the dash lights. Your '04 is likely similar, but I don't know for sure.

Oher issues could be a weak alternator or voltage regulator, or a slipping accessory drive belt. Do you hear a screeching sound when you start the engine or when you accelerate briskly? Time to check and/or replace your belt or belts. If the alternator is weak or if the regulator is suffering issues, either condition could cause lights to fluctuate in intensity, fading from brighter to dimmer and back, either slowly or quickly. If that's what's happening, have your charging system checked and take appropriate measures.

I hope this helps.