Alternator problems

Tiny
JAFAR1771
  • MEMBER
  • 1997 DODGE VAN
  • 220,000 MILES
Had to change the alternator wiring harness connector on the back. Rewired it. Voltage reads 4 on one small terminal and 10 on the other small terminal. Voltage reads overload on b+ terminal. All of this reading while engine is running. Did I wire it wrong? Is the b+ terminal not regulating the charge? It’s not charging the battery at all and the gen light is on in dashboard.
Thursday, June 18th, 2020 AT 9:49 AM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon,

Overload? It should read around 14 to 14.5 volts. Can you verify that?

https://www.2carpros.com/articles/how-to-check-a-car-alternator

That red wire is a feed from the battery for the magnets inside the alternator.

I attached a diagram for you to view. The one wire should have battery voltage. the red one needs battery voltage as well. The other wire comes from the ECM to regulate the charging.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Roy
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Thursday, June 18th, 2020 AT 9:59 AM
Tiny
JAFAR1771
  • MEMBER
  • 9 POSTS
The voltage isn’t going up from 12.2 volts when I turn it on so the alternator is not charging the battery. How do I check if the alternator is getting enough power from the connector to work? What should the voltage from the gen field terminals and b+ wire read and how should I interpret that? Where is the alternator fuse?
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Thursday, June 18th, 2020 AT 10:14 AM
Tiny
ASEMASTER6371
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The black wire should have battery voltage.

The red wire should have battery voltage.

The dark green gets a pulsed voltage from the ECM for charging. Your meter will not pick it up.

The fuse is in the power distribution center and the number is marked on the diagram.

Roy
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Thursday, June 18th, 2020 AT 10:19 AM
Tiny
JAFAR1771
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The new connector that I connected has 2 green wires instead of a red and green wire. Does that matter?
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Thursday, June 18th, 2020 AT 10:25 AM
Tiny
ASEMASTER6371
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Can I have the complete VIN number from the van?

Roy
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Thursday, June 18th, 2020 AT 10:29 AM
Tiny
JAFAR1771
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Thursday, June 18th, 2020 AT 11:17 AM
Tiny
ASEMASTER6371
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Okay, you should have 2 wires that have battery voltage, The other is the field from the ECM. You need a scan tool to turn it on.

Check again to be sure.

Roy
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Thursday, June 18th, 2020 AT 11:32 AM
Tiny
JAFAR1771
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A scan tool to turn the ECM on?
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Thursday, June 18th, 2020 AT 11:37 AM
Tiny
ASEMASTER6371
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To turn on the alternator. The ECM sends a signal down the field for the alternator to work based on load.

A scan tool can turn it from 0 to 100%.

Roy
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Thursday, June 18th, 2020 AT 11:47 AM
Tiny
JAFAR1771
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Are they expensive? Where could I borrow/get one?
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Thursday, June 18th, 2020 AT 11:56 AM
Tiny
ASEMASTER6371
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They are expensive. They run anywhere from $500.00 for a used one to $2,500.00 for a new one.

It would be cheaper to have a shop check it for you. They should only charge you about 1/2 hour labor which should be around $50.00.

Roy
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Thursday, June 18th, 2020 AT 11:59 AM
Tiny
JAFAR1771
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What is the proper way to wire a big gauge ground wire and 2 smaller live wires? I think it’s the connection. How do I tell if I’m getting a good ground connection?
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Thursday, June 18th, 2020 AT 2:19 PM
Tiny
ASEMASTER6371
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You need a voltmeter to test for a ground. Put the red lead on the negative battery cable and the black lead on the alternator itself. Set the meter to DC volts and tell me the reading.

Roy
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Thursday, June 18th, 2020 AT 2:24 PM
Tiny
JAFAR1771
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Black lead just on the metal casing of the alternator?
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Thursday, June 18th, 2020 AT 2:48 PM
Tiny
ASEMASTER6371
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Correct.

Roy
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Thursday, June 18th, 2020 AT 2:51 PM
Tiny
JAFAR1771
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It went in the negatives; -0.1. How do I set it to DC? I just turned the meter to 12v batter section and it already had DC.
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Thursday, June 18th, 2020 AT 4:41 PM
Tiny
ASEMASTER6371
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The ground is good..1 would be the max reading before it would have a bad ground.

No need to run a ground. It is grounded.

Roy
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Thursday, June 18th, 2020 AT 4:46 PM

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