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After installing new battery and alternator the battery goes dead

Tiny
RANDALL729
  • MEMBER
  • 1994 LINCOLN TOWN CAR
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
I just installed a new 1000 amp battery and a new 130 amp alternator in my car. The battery goes dead. I did test the voltage at the battery terminals of the car not running and this was 12.4 volts. With the car running it showed 11.9 volts. I seem to think the reading should have been 14.2. The alternator may be the problem but not sure? There is a guarantee for replacement of the alternator or if it may be the battery there is a 30 month guarantee. Should I approach the parts store about the alternator? Thank you.
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Monday, July 8th, 2019 AT 10:44 AM

3 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

You need to do some testing first before assuming the alternator is the issue.

I attached a wiring diagram for you to view.

Check for voltage at the big wire at the back of the alternator. Make sure it has battery voltage. Check the fuse listed for power with the key on.

Check the third wire for power at the back of the alternator.

Roy
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Monday, July 8th, 2019 AT 11:56 AM
Tiny
RANDALL729
  • MEMBER
  • 59 POSTS
Thank you and problem solved. With car running, getting 14.5 volts at alternator, 14.5 volts at under hood fuse block terminal, 14.5 volts at the positive post of the battery. Actually what I did was clean up the post connections good as before the volts were 11.9 with car running. But I also followed your advice.
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Tuesday, July 9th, 2019 AT 10:40 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Roy
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Tuesday, July 9th, 2019 AT 11:03 AM

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