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PostPosted: Sat Feb 02, 2019 9:48 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
Posts: 6104
Location: So California
Car Model*: 64 Plymouth Valiant
Voltage regulator sends a current to the alternator to tell alternator how much voltage to output.

Check the alternator and voltage regulator grounds.

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes
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PostPosted: Tue Feb 05, 2019 1:18 pm 
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EFI Slant 6

Joined: Sat Aug 23, 2003 8:05 pm
Posts: 254
Car Model*:
Had a bit of time this morning, so first thing I did was test battery voltage 12.56V. Then pulled the green field wire off the alternator and started it. Tested voltage across battery terminals 11.85V, so no ground short in the alternator. Plugged green field wire back in and got almost 19V, then pulled Voltage Regulator wire, and Volts dropped back to 11.85V.

Cleaned the VR grounds but they all looked good and tight, so I went ahead and replaced the Voltage Regulator with the original. Started the car and now have 15.1V with fast idle. Still a bit high, but I will get a new VR and see how it goes.

Found this upon further inspection of relatively new Voltage Regulator:


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PostPosted: Sat Apr 13, 2019 5:13 pm 
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EFI Slant 6

Joined: Sat Aug 23, 2003 8:05 pm
Posts: 254
Car Model*:
Installed a new Voltage Regulator and get the same 15.1 V reading while engine is running.

I better start checking all the connections and negative grounds... Can the ballast resistor affect it at all?


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PostPosted: Sun Apr 14, 2019 5:46 am 
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Board Sponsor & Moderator
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 13366
Location: Blacksburg, VA
Car Model*:
If the battery is a bit low on charge or if not run long, 15.1 V may be OK. Top off the charge on the battery with a separate charger, or switch to another known good and fully charged battery, then check again. After starting engine, you may have let it run/charge for several min for the voltage to come down.

Lou

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PostPosted: Sun Apr 14, 2019 7:22 am 
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Turbo Slant 6
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Joined: Mon Jan 12, 2015 5:55 am
Posts: 843
Location: Brightwood, VA
Car Model*: 1965 Plymouth Belvedere I
Where are you measuring the voltage? It is possible that the voltage right off the alternator may be higher than other places in the system.
Does the voltage skyrocket when you rev the engine? If not, then I agree with what Lou just said, it may be 'normal' on your car.
-Matt

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http://www.MattmansMopars.com
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PostPosted: Mon Apr 15, 2019 2:14 pm 
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EFI Slant 6

Joined: Sat Aug 23, 2003 8:05 pm
Posts: 254
Car Model*:
I tried two different batteries which were fully charged with a bosch smart charger, one battery a year old and the other brand new. Same reading for both across terminals when running, as well as from the positive alternator output terminal and various grounds.

The newest Voltage regulator is actually showing 15.36 V. Seems a bit high, won't high voltage roast all the gauges at some point? Maybe blow up the battery again...

Must be some resistance through a poor connection somewhere.


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PostPosted: Wed Apr 24, 2019 12:15 pm 
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TBI Slant 6

Joined: Sat Mar 19, 2016 7:25 pm
Posts: 172
Location: SW PA
Car Model*:
You have to check for a voltage drop between the batt. post on the starter relay, and the blue ign. regulated voltage wire that runs to the alt., ballast or (?) ign., and the reg............any of the connections from both bulkhead pass-throughs, ign. sw. & connectors etc. have to be checked for a drop. If the reg. is seeing 14V at the blue wire, but the batt. is at 16~18V, it's not going to stop charging at that rate.


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