Unpredictable battery light

Hi all,

I have a Ford Taurus 1993, GL station wagon with 240K miles on it. About six months or so ago, its battery light started to flash on low rpms. I took it to a mechanic and he changed the alternator. When I drove it back home, the light was off and remained off for almost a month.

Then it started again and frequency and duration increased. It is interesting to note that all these months there was never a problem with starting the car. For last few days, the light finally has become steady (does not flash with change of rpm) though it is dimmer than what you would think would be a normal red light on the Ford Taurus instrument panel.

I do not know if this is a false alarm, or I really have a problem which would simply make the car not start one morning.

Please advise.

Shaun

Checked the battery? An old battery or one about to fail may be giving you a warning signal.

That light depends upon voltage out put from the alternator to be "off". As the voltage at the alternator output starts to fall, enough current starts flowing through the lamp to make it visible. With no output from the alternator, the lamp will be fully lit. Same thing happens, though, when the battery has a short. So, you need to pull the battery and put it on a tester to see if it's good. If so, have the alternator tested as well.

A voltmeter test of the battery will help out. While the car is on the alternator should be delivering about 13.5 volts or so to the battery terminals. If it is lower than this then the charge lamp is indicating a real problem. I turn on the lights, blower motor, radio, etc., to check the voltage regulation as well. It should not drop much even with a full load. A good battery will indicate a voltage of about 12.5 volts after the car is turned off.

If you are starting and driving OK then the battery is probably being charged up. Bad batteries or those not being charged tend to die off fairly quickly, especially when the head lights are on.