1999 Ford Truck Dead battery

AHMORNING

MEMBER
1999 FORD TRUCK
4 CYL
AWD
AUTOMATIC
16,200 MILES

I have a 99 F-150, we have replaced alternator and battery. The battery is still draining quickly. Have taken to repair shop and were told it was a bad alternator. We took the alternator back to parts store where they tested it and said it was fine. Does anyone have any ideas as to why the battery is still draining? Please help.(Can't afford another trip to repair shop, alternator and battery cut into our funds)

4 Replies

RASMATAZ

MECHANIC
75,992 POSTS

There's probably a short somewhere in the electrical system that's draining the battery.

Battery drain test:

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Saturday, August 22nd, 2009 AT 2:13 PM

JDL

MECHANIC
16,098 POSTS

Hello, did the store check the alternator on or off the vehicle? If it was off, it is possible the alternator is good, maybe a problem with the alternator wiring circuit? With everything turned off, it is possible you have a battery drain? I don't have the specs in front of me, for the allowable drain, usually well less than 1/2 amp.

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Saturday, August 22nd, 2009 AT 2:18 PM

AHMORNING

MEMBER
2 POSTS

They did check the alternator when it was off. Also, they have checked for a battery drain. I was thinking the wiring between the alternator and battery, but I'm not really sure.

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Saturday, August 22nd, 2009 AT 2:37 PM

JDL

MECHANIC
16,098 POSTS

If you have a digital multimeter, you can check the charging system. With everything turned off, take a reading across the battery posts. The generic figure for a fully charged battery is around 12.6 volts. Then start the vehicle, take a second reading across the battery posts, the second reading should be higher than the first, if it isn't, take a reading at the bat terminal of the alternator, see how it compares to the battery reading.

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Saturday, August 22nd, 2009 AT 3:02 PM