Lights dim as rpm goes up? Options

[koozy]

What the heck? I never drove my car at night until tonight. I get in and start the car. Drive down the street and notice the lights are kind of dim but not too bad. I step on the clutch and when the rpms go down to idle the lights get brighter. So I pull over and check it out. The lights dim as I increase rpm and when I let go of the gas and come to idle.... 3 seconds or so after it's at idle they get brighter. I've seen the opposite happen but never this. What could be happening?

[geniusanthony]

It sounds like your alt. is not charging. If you recently pulled the motor like I did once and did not plug the harness back in to the relay board, there should be a red light on your fuel/combo gauge with engine off and key in the run position for at least a few seconds. Another check for your charging system is battery voltage w/ engine off vs. engine running....,i.e., ~12v.- ~14+. After those checks, do you have high power driving lights or high wattage bulbs but that shouldn't affect this.

Good luck, been there.

[purple]

make sure you're using a proper light bulb in the alt warning light socket, not an LED. and make sure it's not burned out.

The charging system works through this light bulb

Make sure fuse #9 is there and not blown either

[koozy]

I did forget to check the alt light on the instrument panel when I turn the key on. I also failed to mention it was the headlights that dim. I didn't look to see if the instrument panel lights do the same thing. I'll have to look tonight. Got to skidadle to work now. Thanx for the advise so far. I'll let you know about the instrument panel lights.

[2-OH!]

As mentioned above, use a multimeter and check the voltage on the battery post, engine running and shut off (as in, Key in your pocket off)...Should read 13.5+ and at least 11.6+...

If it's the first, then you have charging issues...If it's the second, you got battery problems...Could have both...

Be sure to check the ground wires directly behind the headlight buckets, near where the linkage goes through to raise and lower...

2-OH!

[Spoke]

I had this same thing happen on my 74 Dodge Colt. Lights dimming at night, battery discharging. Let it idle and the alternator slightly charges the battery. Rev the engine and it discharges. WTF?

I took the alternator apart, put an ohmmeter on the armature through the brushes. Had low resistance not spinning. Spin with my hand and the impedance went up. Not good. The current through the armature sets up a magnetic field that gets picked up by the stator (stationary windings around the armature) which produces the voltage.

My fix since I was in college and poor, was to remove the brushes, clean them and clean the contact area on the armature since it was very dirty from about 8 years of use. Brushes were worn but not shot.

Put it back together and into the car. At this point my battery was just about dead so all parking had to be done on a hill to clutch bump start it. Bump started it and at idle I had more than 15amp charging. Rev'ed the engine and charging went above 30amp.

Unless you feel like ripping your alternator apart, go get a new one.

Spoke

[Air_Cooled_Nut]

It's because you're driving too fast and approaching the speed of light. Slow down!

Geez, kids these days, no respect for general relativity... (IMG:style_emoticons/default/shades.gif)

[jd74914]

In my experience battery issues usually mean that the lights dim when you are NOT revving (ie: they are dimmer at idle than at reline) because the battery doesn't hold enough charge to run the entire system at full blast.