Need help alternator problem

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jaybale23

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I recently went to gas up my 72 mustang and when I went to restart it, the battery was not strong enough. The battery is less than 3 months old. Then I noticed the Alt gauge was flat on the D. So I changed the alternator and the voltage regulator. It did not fix it. When car is running and I pull the negative from the battery it instantly dies. Now the alternator light is on too. When I check the voltage to the regulator the ignition wire only shows 1.6 volts. Everything else is 12.5. I feel like it might be a wire issue. Any suggestions on where to look next are appreciated. Thanks in advance.
 

midlife

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That ammeter looks to be a voltmeter (not centered) and not hooked up, as both the temp and oil pressure gauges are reading something. Or your battery is desperately low, like 6-9 volts.
 

Paul M

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Did you change the alternator to a different brand? I noticed they route the wires differently between the power master and the other brand. One start up w/ the wires crossed, and you'll fry the voltage regulator.
Try a voltmeter on the battery with the car off it should be slightly better than 12v (12.6 is nice) Check while idling and look for between 13 & 14.5v. If that's ok, put the meter on the S terminal of the alt and look for 14v+.
Pull your regulator plug while the car is still running and jumper the Field wire to your positive terminal. This will "full field" the alternator and your voltage should shoot up. If it does your regulator or wiring has an issue. If not then your alternator has an internal problem. Do not leave the jumper on very long or you will overheat youR alt and fry a diode. I had brand new regulator go bad last month. Our new parts we are getting, leave much to be desired NOWADAYS.
 

jaybale23

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I did go to a new brand. Had to change up how it was connected. Thought I wired it correctly but wouldn’t hurt to revisit.
 

jaybale23

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That ammeter looks to be a voltmeter (not centered) and not hooked up, as both the temp and oil pressure gauges are reading something. Or your battery is desperately low, like 6-9 volts.
The picture was right after I got a jump. So the battery was very dead.
That ammeter looks to be a voltmeter (not centered) and not hooked up, as both the temp and oil pressure gauges are reading something. Or your battery is desperately low, like 6-9 volts.
The picture is right after a jump. So battery was really dead.
 

Hemikiller

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When car is running and I pull the negative from the battery it instantly dies.

Please don't do this, it's a great way to cook electrical components.

You state you have an alternator light as well as the center gauges? Based on that alone, it means someone added the gauges and you have some "custom" wiring in place. Lets get a couple pics of the wiring in and around the voltage regulator.
 
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Sounds like a fusable link let go or you lost a connection from the alternator power post.

That or engine ground.

With the engine running out a meter from the alternator battery terminal and the negative meter lead to the case.

Should be over 12v

Possible bad new alternator or a wire crossed
 
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