Alternator grounding Question

[Polsky]

My car is a 1967 Dodge Coronet RT. When I bought the car it had no motor. I have since installed a healthy 68 440, new battery, and new alternator. The battery keeps going dead. I have 12.5+ volts across the terminals whether it is running or not. I have the older style voltage regulator and the rest of the wiring is what seems to be stock besides electronic ignition. The wires going to the alternator are the one field (on the alternator bolt), the power for the horn relay (on the alternator bolt), and the one wire that is has the plug in for the spade terminal. I see the new alternator has a ground screw. I know this is a silly question but do I have to ground the alternator? Any other trouble shooting tips would be appreciated. Today (Saturday) is my son's birthday party. I promised him a ride in the car, which has not been over a block since I got it running. I just do not want to break down with him in the car. Any help would be appreciated.

Cheers,

Frank

 

[kiwigtx]

Hi there,
My friend went through a similar experience this week. An older car with a factory single field alternator wiring loom upgraded to a new two-field Alternator. If there is only one field wire available, on a two-field alternator, simply connect one field to ground - doesn't matter which one, as they both serve the same purpose. Follow the drawings below and it should be helpful to you;

Normally you should see around 13.8 volts while engine running at fast idle, and up to around 14.6 max at full engine speed. See how that goes.

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a little bigger.....

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You should see that the Alternator is grounded due to the fact it is bolted to the engine - however a continuity test will prove how good that grounding is. It would not hurt to install a wire if required.

 

[Polsky]

How can you tell if it is a single field? The new alternator has the post, spade connector, and ground. Is this still a single field?

 

[62 Dart Convertible]

How can you tell if it is a single field? The new alternator has the post, spade connector, and ground. Is this still a single field?

Sounds like it. Post a pic of back of alternator...

With engine off, measure battery voltage. Start the engine and check the voltage to ground (with a voltmeter) on the field terminal whilst head lights are on. If it is close to zero you have a problem with regulator or assoc. circuit. If it is close to 12V and alternator does not raise battery voltage above what it was before starting, then alternator is faulty. If you suspect alternator is faulty, check resistance of field terminal (with regulator wire disconnected) to ground - it should be several ohms. If open circuit, field winding is stuffed. Alternator does not normally need grounding specifically as the mountings should earth it sufficiently well unless paint is insulating it as such.

 

[Polsky]

I will work on posting a pic of the alternator. What I was able to get done is the battery voltage is around 12.5 volts when not running. The field wire to ground is around 3.5 volts running with the lights on and the battery does not raise. Seems like a weird voltage.

 

[Polsky]

Thanks for the help so far. I know I still owe you a pic, trying to find the time to take the alternator off. I ended up changing the voltage regulator. I took the old one apart and it was cooked. I am still only getting around 10 volts to ground off the field at 900 rpm's. Some of the connections were corroded so they were replaced tonight. It is to late to start up the car and verify if this changed anything. I am hoping to get a pic of the back of the alternator tomorrow. When shining a light on the back of the alternator I did notice a threaded hole in the casting that said field but did not see any connection for it. Again, I will verify.

 

[Polsky]

Got it figured out. Come to find out it was a combination of a bad voltage regulator and a the field wire being partially broken and corroded inside the connector. Thanks for the pointers folks. I appreciate it.

 

[62 Dart Convertible]

Got it figured out. Come to find out it was a combination of a bad voltage regulator and a the field wire being partially broken and corroded inside the connector. Thanks for the pointers folks. I appreciate it.

I love a happy ending! Congrats mate..