Mechanics

88 T-BIRD ALTERNATOR WORKS BUT NO CHAGING AT BATTERY

1988 Ford Thunderbird • V8 2WD Automatic • 200,000 miles

1988 T-bird alternator works but does not charge the battery. Battery accepts lasting charge from 120vt wall charger. Battery light on when ignition turned on but goes out when engine started. Believe its a wiring problem but can't find an issue. Believe the fusible link for the alternator is a 20 gauge blue wire connected on one side to a yellow wire that seems to go to the alternator, and on the other to the main fusible link on the starter relay. Any help appreciated.
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Jmk6753024
August 12, 2011.




Measure the voltage on the output terminal when the engine is off. You should find battery voltage there. If it's 0 volts, the fuse link is open but that's not going to be a 20 gauge wire. That will be closer to a 10 or 12 gauge wire.

If you have battery voltage there, measure the voltages on the other wires and holler back.

Caradiodoc
Aug 12, 2011.
UGGGHHH! I just looked up your generator and I see it's the one with two output wires plugged into the side of the case. That is quite the design. That plug is supposed to never be disconnected. Doing so will degrade the terminals and lead to them overheating and failing. Replacement generators come with that plug already installed. You are supposed to cut the wires and splice the new ones to the car's harness.

The fact the battery warning light goes off when the engine is running proves the generator is working. Close to half of battery voltage will appear on the white wire when the unit is generating an output. That tells the regulator to turn the light off.

Back-probe one of the black / orange output wires to read the voltage while the engine is running. If you find between 13.75 and 14.75 volts, it's working. Measure the battery voltage next. If it's lower, near 12.6 volts, current isn't getting back to the battery. Look for a fuse link that's burned open.

If you find 12.6 volts or less at the output wires, those terminals have burned up. The repair will consist of trying to clean and shine them up and replacing the connector. If that repair fails, you'll need to replace the generator.

Caradiodoc
Aug 12, 2011.
DOC,

WE HAD SIMILAR PROBLEMS WITH MY PAP'S 86

TURNED OUT TO BE THE CONNECTOR AT THE VOLTAGE REGULATOR WAS NOT MAKING GOOD CONTACT. IT'S A REAL CRAPPY CONNECTOR THAT FORD USED FOREVER.

IT'S BEEN A LONG TIME, I THINK I USED A TEENY-TINY CRESCENT WRENCH (I KEEP IN MY POCKET, ALONG WITH A MINIATURE CHANNEL LOCK PLIERS, REVERSIBLE SCREWDRIVER, AND POCKET KNIFE!). ANYWAY I SLIGHTLY BENT THE TERMINALS DOWN THE ROW, TO PRESSURE AGAINST THE OTHER HALF. IT'S SORTA OBVIOUS, WHAT TO DO!

MAYBE THIS HELPS, MAYBE NOT. THOUGHT I'D SLING IT OUT THERE ANYWAY!

THE MEDIC
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CJ MEDEVAC
Aug 13, 2011.

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