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Alternator wont charge

Tiny
UTAHMARK
  • MEMBER
  • 1995 BUICK PARK AVENUE
  • 167,000 MILES
Have a 1995 buick park avenue with 3800 series II motor. Rebuilt the motor and put back in, car runs, but alternator is not charging. Had the alternator tested and was fine. Brand new battery. It will charge if I run a jumper from the positive on the battery to the plug in on the back side of the battery (only one wire). As soon as I unhook it it stops.I have.04 volts on the wire that goes to the plug in. All fuses tested and replaced. What could cause it? Wiring all looks good as well
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Saturday, December 31st, 2011 AT 10:36 PM

17 Replies

Tiny
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****jumper to the back side of the alternator. Sorry****
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Saturday, December 31st, 2011 AT 10:37 PM
Tiny
SATURNTECH9
  • MECHANIC
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So your jumping a wire to the black large wire that has a nut holding the wire to the batt post of the alternator?
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Saturday, December 31st, 2011 AT 10:51 PM
Tiny
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No. That wire goes directly to the battery from the reg. Im jumping a wire from the bat + to the plug with one little red wire and the alternator that feeds from the main wire harness coming from inside the vehicle. Also put a new ecm in
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Monday, January 2nd, 2012 AT 7:40 AM
Tiny
SATURNTECH9
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So you havent check the resistance with both ends of that wire unplugged and see if there is two ohms or less end to end?
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Monday, January 2nd, 2012 AT 8:29 PM
Tiny
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Checked it today. No resistance. To and the main wire harness on the firewall. The pin that goes to the alternator show. 12.5+/- but as soon as I plug it back in the alt wire shows only.01 volts. I also to the main wire harness on the engine side and did a jump wire from the alt pin to the battery, hooked my ground for my voltmeter up to the battery, and tested the wire for voltage that way on the pin by the alt and had 12.5 +/-
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Tuesday, January 3rd, 2012 AT 1:30 AM
Tiny
SATURNTECH9
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So did you unplug the ecm computer and the connector to the alternator and measure the resistance on that wire from the alternator to the ecm connector to connector?You should see 2 ohms or less.
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Tuesday, January 3rd, 2012 AT 1:58 AM
Tiny
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Ill have to check that but when I turn the key on I have power from the ecm side of the wire harness to where the alt pin would slide in
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Tuesday, January 3rd, 2012 AT 4:42 AM
Tiny
SATURNTECH9
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You said earlier you only had .04volts to that wire now you say you have 12 volts sounds like a wire or loose terminal issue. Check like I suggested and let me know what you find.
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Tuesday, January 3rd, 2012 AT 5:00 AM
Tiny
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With the harness complete I have.04. When I take the engine harness off the firewall where it hooks up and turn the key on, I have 12.5 on the firewall for the pin coming off the computer harness for the alt. Inly with the harness complete do I have the.04 at the alt
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Tuesday, January 3rd, 2012 AT 11:03 PM
Tiny
SATURNTECH9
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If you have 12 volts at the ecm pin but only.04volts thru the harness at the alternator then you need to check that harness. Have done a resistance check like I said?If so what the ohms reading?
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Tuesday, January 3rd, 2012 AT 11:11 PM
Tiny
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.001
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Tuesday, January 3rd, 2012 AT 11:28 PM
Tiny
SATURNTECH9
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What scale was the meter set on?If you have a 200 ohm setting I would have set it there.
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Tuesday, January 3rd, 2012 AT 11:51 PM
Tiny
SATURNTECH9
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You might just have to run a new wire from the ecm.
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Tuesday, January 3rd, 2012 AT 11:52 PM
Tiny
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Thats what I was thinking, but taking and running a wire from the drivers side fuse panel from a switched wire with a 15-20 amp fuse to the back of the alt
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Wednesday, January 4th, 2012 AT 6:45 AM
Tiny
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Do you know which connector and pin on the ecm it is for the alt wire?
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Wednesday, January 4th, 2012 AT 6:46 AM
Tiny
SATURNTECH9
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No the ecm regulates the voltage for the ecm so run a new wire from the ecm.
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Wednesday, January 4th, 2012 AT 6:51 AM
Tiny
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If you dont know which pin it is on the ecm how did you check that wire for resistance?
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Wednesday, January 4th, 2012 AT 7:13 AM

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