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Long one here ! I finished restoring my engine compartment and reinstalled my newly rebuilt 289. She runs great, BUT !!! I have an electrical problem. My alternator is only putting out 11.73 volts according to my multimeter. Now the result: The Sears Security battery has a power saver feature which shuts it down if it reaches about 11.5 volts (like in case you left your lights on). The car starts ok, but then the battery shuts down after 5-20 minutes because it is not getting enough juice. The alternator, voltage regulator and starter solenoid are new and correct. Also each of these components has been bench tested at a reputable auto store and all check out great. Also used a new alternator harness, battery cables, etc. I even tried the old alternator, voltage regulator , etc. What is going on ???? Why would the alternator put out 14. 75 volts on the bench test and only 11.73 on the car ??? I tested at the alternator (on the car running) and at the battery, both give around 11.73 volts. I can rearm the battery each time it shuts down, but this won't last for long. SOMEONE at the auto store suggested it may be the ignition switch. He said the ignition switch "excited " or sent a signal to the alternator enabling it to charge ????Also just a few minutes ago, I smelled an electrical burning under my drivers side dash. Could not visually spot the problem. And the engine still starts and runs for a few minutes till the battery shutdowns from too little voltage. Also tried a new replacement SEARS Security battery with same results a few days later (after its voltage dropped from low alternator output). HELP !! I am pulling my hair out. I know turbine engines real well (see profile) but this one has got me going crazy. Thanks to all in advance. This is a great forum. Miss the old one though. Brad

<P ID="edit"><FONT SIZE=-1>Edited by 1967Pony on 03/10/01 11:40 PM (server time).</FONT></P>
 
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The alternator requires current going through the rotor to charge. Check to see that you have voltage going to the rotor. That will tell you if it's the regulator circuit or maybe a bad ground. It's also posible that the alternator is overloaded and not able to produce enough current. That requires a current probe to measure the output of the alternator. I believe it's safe to disconnect the output lead though, then you could measure the no-load output. If you've got a restomod with electronic ignition then you need to be carefull when disconnecting not to cause a surge. Hope this helps.

Adrien.

<P ID="edit"><FONT SIZE=-1>Edited by stangs4me on 03/10/01 11:33 PM (server time).</FONT></P>
 
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I don't have a restomod. The rotor is new. The alternator passes all tests on a test machine under load and with no load.
 
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What stangs4me is trying to say is that here should be a magnetic field present in the alternator. The alternator has no permanent magnets but electromagnetic ones. The field is produced by a current flowing through a coil. When this current is too low (caused by bad contacts) the output will be too low.

In the bench test the alternator+VR worked, so the problem lies with the rest of the electrical system. Clean ALL contacts thoroughly an test again.

Unlike a regulator for a generator, an alternator-VR only has to regulate the voltage. The current will sort itself out depending on the current demanded by electrical equipment. When there is an overload (more demand than the alternator can supply) the shortage will be drawn from the battery, eventually leading to the results you experience. You also mentioned you could smell something burning/melting under the dash. That's the first place to check because a burning smell is a REALLY BAD sign and may be the cause of the overload. It may be caused by a short.
 

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You have a massive short under the dash, which pulls excessive current, which draws the voltage down on the battery/alternator. You are about to have an electrical fire.

Start by pulling fuses one by one to isolate the problem. First, charge the battery, then check voltage there. Put key to ON, and check voltage. Does it start to drop? Pull fuses one by one. If problem only exists when engine is running, then do the same, but briefly, as you are about to set things on fire under the dash. Good luck.

You can also use a ammeter between the negative battery post and the disconnected negative battery cable. With key out, all doors closed, you should see less than 10 milliamps of current. Anything more indicates a short or something is on, draining the battery. You can use this test with the key in ON or ACC position too. Do not do this test while car is running.

http://clubs.hemmings.com/baymustang/flamicon.jpgLet me check your shorts! My multimeter is just a-waiting! Formerly known as Midlife in the old VMF.
King of the Old Farts *struts*
 
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Interesting problem. The burning is of concern - had that in an F-4 cockpit in 1972 - scared the bejeebers out of me. Sounds like you have an in-dash ammeter rather than an idiot light. The harnesses are different - do you have the right one ?? Three-wire VR connector for the ammeter; four-wire for the idiot light. What are your cockpit indications on the light/ammeter ?? Would like to follow your adventure - come back with an updated post.
 

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This is only a guess, but are you absolutely sure that your alternator/regulator wiring is correctly hooked up?

67 Vintage Burgandy 390GTA with most of the bells and whistles
 
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