Dimming lights. Alternator? Battery?

[mattocs]

Sometimes when i'm sitting in traffic or something and I press the brakes, I notice my headlights dim. When I hit the gas and let the engine rev up a bit, they get bright when i'm just sitting there.

 

I had my headlights on with the car not running for like 15 minutes, which drained the battery.

 

New alternator belt? Alternator not working, and needs replaced? Battery not holding a charge to well?

 

Let me know what you folks think, as I am going to be adding some serious driving lights soon and will need all the power I can get.

 

Thanks.

[NOMAD327]

Batteries last three to seven years depending how good they were to begin with, that's with everything else working properly, your's may just be getting near the end. Radio Shack sells a nifty tester for about $5, it's a set of wires and a series of LED's. First you connect it to the battery without the motor running and it will tell you battery condition. Then you start the car and test it again and it will tell you how charging voltage is. If it has low battery voltage but is charging fully, drive awhile and see if the battery voltage comes back up. If not, there are a number of things to check, The most common problem for this sort of thing is loose or corroded battery terminals. You can check the water level in the battery cells, but this is not a big issue like it used to be and is seldom the cause of any problems. Unhooking the battery wires will loose radio and clock settings, and on models from about 95 to 98 with keyless entry, will trip a blinking parking light/horn which will need thee key fob to turn off. Other things would be a loose drive belt, ours do not have spring loaded tensioners like a lot of cars, so they may need to be tensioned a week after initial installation, and maybe once more after a few years. Loose belts normally squeal for a moment on startup, especially if it's a damp day. The ground wire should be checked where it attaches to the body and any ground wires between the engine and the body should be in place. start with that stuff.

[nipper]

Actually with everything on diming a bit at a traffic light is normal. Altenators dont put out max power at idle, and with everything on you are drawing alot of current. Sometimes the act of putting the car in neutral is enough to bring upp the power. Any autoparts stroe will put a load tester on your battery (looks like a big silver shoe box with 2 jumper cables) and test them fro free. Watch over the guys shoulder, as this is a test that they cant fake to seel you something you need. It will tell you battery response to a load, running, and when actually cranking.

 

This is a standard test. If your bettery is more then 4 years old, 3 years in an extreeme climate, i agree it may be starting to fel its age, but not because of the dimming.

 

nipper

[edrach]

Alternators put out less volts at idle; so that's normal. However, it can also be an indication that the alternator is not charging the battery enough or the battery is not taking a full charge. Most autoparts stores will offer a free check of your car's electrics. Of course they are biased to sell you the parts, but a check at two or three shops should allow you to decide what you need.

[fishy]

Here's a simple charging system check I like: stick a voltmeter on the battery while the car is idling. it should be making more than 14 volts. I believe my high-mileage, emergency backup alternator made about 14.3 when I checked it like this. The failing original was making 13.5 under the same test circumstances. It's a quick and easy test though.

[mattocs]

Thanks for the suggestions. The battery is a 'no maintinence' Carquest brand cheap-o that is 3 or 4 years old.

 

I think i'll replace the battery and alternator belt and see if they helps any.

 

Thanks again.