Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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Joined: Feb 2007
Posts: 570
Oil Can Mechanic
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Oil Can Mechanic
Joined: Feb 2007
Posts: 570
On my winter car, the battery is getting run down over night. I put a meter in between the + post of the battery and cable. I pulled all the fuses one by one, and it still indicated a draw. One of my friends had a past experience with the regulator shorting out internally. It has an externally regulated alternator. My regulator was old STANDARD part, so I replaced it ($12 American) figuring it would be a wise idea anyways. I then decided to run the engine and check voltages. I had 3.5v at the field terminal of the alternator. Is this normal? I didn't think there should be any voltage there at all, being that it will eventually find itself grounded. Am I confused or is this a bad alternator?

Joined: Jan 2008
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ChatMaster - 750
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ChatMaster - 750
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First what are you working on? Yes it could be in your alt. just unhook the wires. Are you using a volt or amp meter? I had one once at the shop that had main hot wire off the starter that was pinched just enough to cause a draw and then got bad enough to blow the fuse link.


Dens Chevys 1927 Speedster 1928 coupe 1941street rod 1947Fleetline 4 door 1949 1/2 ton Pickup (sold) 1954 210 4 door 1972 Monte Carlo 2003 Corvette convt..
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ChatMaster - 25,000
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ChatMaster - 25,000
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It can be caused by a bad diode in the alternator.


Gene Schneider
Joined: Feb 2007
Posts: 570
Oil Can Mechanic
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Oil Can Mechanic
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Posts: 570
If a diode is bad would that allow a discharge of the Battery? or just not rectify the current from the windings?

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ChatMaster - 25,000
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ChatMaster - 25,000
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A diode is like a one way valve or like the cut out for the generator. On the older cars the GEN light would come on when the ignition was turned. Then you knew a diode was bad. The rectifier converts the current.


Gene Schneider

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