Battery power...lights dimming.

[kimi03]

98 SC2. 120,000 miles. I have a brand new battery and haven't had any problems with the car starting or anything, but if I'm driving at night sometimes when I touch the brakes the dash lights dim quickly but then go back to normal. This also happens when rolling up the windows. If I'm parked I can hear a change in the engine when rolling up the windows too.

Is this anything I should be really concerned about if there aren't any problems otherwise? If anyone else has had an experience like this it would be great if you could share if you had any problems.

[HAWG]

you may want to have the charging system checked to be sure the alternator is charging correctly. May not be putting out enough under a load

[drew300]

And check the battery connections. I had a similar problem that was just a loose connector.

[saturnspeed_12]

corrosion on battery terminals, bad ground, loose connections, or bad alternator.

[timber284]

Originally Posted by kimi03

98 SC2. 120,000 miles. I have a brand new battery and haven't had any problems with the car starting or anything, but if I'm driving at night sometimes when I touch the brakes the dash lights dim quickly but then go back to normal. This also happens when rolling up the windows. If I'm parked I can hear a change in the engine when rolling up the windows too.

Is this anything I should be really concerned about if there aren't any problems otherwise? If anyone else has had an experience like this it would be great if you could share if you had any problems.

I have the same exact problem with a 96 SL1 with 103,000 miles. I used a volt meter to check the battery on a very cold day and while under load and its fine. Next step is to have my alternator checked. My lights dim and go back to normal when on turn on the blinker, the rear defrost, etc.

I found the following alternator test on the web:

1. Start car and run at normal idle.
2. Connect voltmeter to battery terminals.
3. Turn on headlights to high beam.
4. Check battery voltage. Should be between 13.8 and 14.2, possibly up to 14.5
5. Increase motor speed to 1500 rpm. Alternator should now produce a battery voltage between 14.2 and 14.6. If its lower than 14.2, the alternator probably has one or more bad diodes.
6. Now, maintain 1500 rpm and turn off headlights. Run test for one more minute. Battery voltage should never exceed 14.8 volts. If it does, alternator is probably bad and is over charging battery.