battery light is on on 1998 Mercury Grand Marquis

new alternator (2-3 mo); new battery (installed today); new serpentine belt; new belt tensioner all changed today...but the battery light is still on (the red warning light on the dashboard). does it take time for the battery warning light to go off?

by in Cordova, TN on October 26, 2010
2 answers 1 comment
ANSWER by on October 26, 2010
no. check the wire ends on the alt. there is a connector with one single wire that tend to be a bad connection and trigger the light. by the way, did you check the voltage while running?? Roy
ANSWER by on October 26, 2010
Roy is right! It could be a bad or unsecured battery ground cable between the battery and chassis or chassis and engine. Turn on the ignition switch to the on but not run position do you see an icon on the instrument panel representing a battery, if you do not see this battery icon the alternator is not seeing power to allow it to charge. Start the engine does the battery icon go out. A more complex but good diagnostic test is checking "voltage drop" on the battery ground and power cables. You can find a video on how to do a voltage drop test on youtube. Put a volt meter across the battery terminals with the engine off, at rest the battery voltage should be 12.6 volts if the battery is fully charged. Now get a friend to start the car while you watch the voltmeter, the voltage reading across the battery should read approximately 14.6 volts if the alternator is charging correctly.
COMMENT by on June 01, 2013
I realize this is an old thread, but I noticed one thing in your reply that may be my problem. You said "Turn on the ignition switch to the on but not run position do you see an icon on the instrument panel representing a battery, if you do not see this battery icon the alternator is not seeing power to allow it to charge." My 98 Grand Marquis voltage gauge started intermittently dropping and the lights would dim. I replaced the alternator and the 3 pin pigtail since it was cracking. I still have the same problem with the voltage intermittently dropping. I tested the battery, charged it overnight and even tried a new battery in it. So after reading your comment, I looked at the dash with the key on and engine not started. There is no battery light. What causes this to happen? What should I be looking for? Thanks for any help.
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