dim light quiz

[BennyM]

Lights in dash dim slightly when ignition turned off. Does this signify:

A. Bad alternator or voltage regulator?
B. Worn/dirty brushes?
C. Bad Battery?
D. Normal operation?
E. None of the above?

Sorry-- midterms week.

Thanks,
BennyM

[632 Regal]

Lights in dash dim slightly when ignition turned off. Does this signify:

A. Bad alternator or voltage regulator?
B. Worn/dirty brushes?
C. Bad Battery?
D. Normal operation?
E. None of the above?

Sorry-- midterms week.

Thanks,
BennyM

[Mr Project]

I agree with D.

Battery output voltage is 12.6 (?) at best, alternator output voltage is 13.3-14.4, so of course the lights will be slightly brighter when running off alternator output vs. battery output.

[Paul in NZ]

that the battery is getting old...a fully charged "12v" lead acid battery can be as high as 14v......

[Javier]

there is poor connection on charging system or battery (+ or -). If severe, lights dim out also when running idle and go back to normal when revving up.

[BennyM]

there is poor connection on charging system or battery (+ or -). If severe, lights dim out also when running idle and go back to normal when revving up.

Yes, it does this sometimes. If I rev the engine, the headlights will get slightly brighter for a moment. They don't dim out. This is simply a bad connection?

[BennyM]

nt

[Jon K]

The battery only holds a 14v charge when the alternator is feeding it... otherwise, the battery should hold 12.0 +-.5 volts when on its own... but that's rare. Even new batteries hold just below 12.0. Unlock your OBC and see what I mean. If I do Test 9 on OBC with car in Pos. 2, i get 11.98v which will slowly drop (with radio on, subs, etc) to about 11.4 until I turn it off. Even when running the car, my alternator makes abour 12.94v until i blip the throttle and then it will jump to like 13.86 - 14.09. I know these numbers by heart ever since I had alternator woes.

[BennyM]

The battery only holds a 14v charge when the alternator is feeding it... otherwise, the battery should hold 12.0 +-.5 volts when on its own... but that's rare. Even new batteries hold just below 12.0. Unlock your OBC and see what I mean. If I do Test 9 on OBC with car in Pos. 2, i get 11.98v which will slowly drop (with radio on, subs, etc) to about 11.4 until I turn it off. Even when running the car, my alternator makes abour 12.94v until i blip the throttle and then it will jump to like 13.86 - 14.09. I know these numbers by heart ever since I had alternator woes.

I am not super worried about it. My OBC gives me almost the same numbers. Just out of curiosity, where in the line is this measurement coming from? The battery terminals? Alternator? Some arbitrary grounding?