The Ford Barn

Chris Smith · 07-27-2014, 06:31 AM

I have a 31 A that was successfully converted to a 12 V Positive Ground. I was having problems with the alternator and changed it out for a new 10SI, 60 amp unit. Easy one wire install, but had bad results when going to jump the car. I think I need a positive ground alternator. I know there has been some debate on the reality of a positive ground alternator on this blog so I am asking again. Is there a need to run a positive ground 10SI alternator in a positive ground installation?

Mike V. Florida · 07-27-2014, 06:39 AM

If you car is wired positive ground you need a positive ground voltage source, Negative ground a negative ground voltage source.

BRENT in 10-uh-C · 07-27-2014, 07:43 AM

Hey Chris, welcome to Fordbarn.

Personally, if you have had issues jumping a positive ground system, the cause is 'operator error' and really not the fault of the system, but that's ok but just know a positive ground system CAN be successfully boosted off of a negative ground system.

If you do decide to reverse the polarity to a negative ground, the only two things that really needs to happen is reverse the polarity on the coil by exchanging the two wires and place them on the opposite respective terminals, and to reverse the wires on the backside of the ammeter. Hopefully your battery cables are long enough to be reversed too, but that should get you to a negative ground.

Since the 'one-wire' alternator has an internal self-exciting regulator that always has a current draw on the system, you might consider installing a disconnect switch to interrupt the current when the vehicle is not in use. Another alternative is to install a Model-A generator back on there with a diode equipped cut out and an EVR installed internally where you can eliminate the about half of your headaches and allow the engine compartment to look more aesthetically correct.

Again, welcome to the Forum here!!

Charlie Stephens · 07-27-2014, 10:55 AM

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I would consider changing the ground over to negative if you have to replace the alternator. Some of the advantages of the 12 volt alternator are lost when you go positive ground such as many of the negative ground alternators are for modern cars and are over the counter at a parts store if you need one on the road and some modern electronics are polarity sensitive which means you should have a negative ground system.

Charlie Stephens

07-27-2014, 06:31 AM	#1
Chris Smith Junior Member Join Date: Jul 2014 Location: Wakefield, RI Posts: 1	Positive Ground Alternators I have a 31 A that was successfully converted to a 12 V Positive Ground. I was having problems with the alternator and changed it out for a new 10SI, 60 amp unit. Easy one wire install, but had bad results when going to jump the car. I think I need a positive ground alternator. I know there has been some debate on the reality of a positive ground alternator on this blog so I am asking again. Is there a need to run a positive ground 10SI alternator in a positive ground installation?

07-27-2014, 06:39 AM	#2
Mike V. Florida Senior Member Join Date: May 2010 Location: Florida between Sarasota and TampaSouth Florida Posts: 14,054	Re: Positive Ground Alternators If you car is wired positive ground you need a positive ground voltage source, Negative ground a negative ground voltage source. __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

07-27-2014, 07:43 AM	#3
BRENT in 10-uh-C Senior Member Join Date: May 2010 Location: Eastern Tennessee Posts: 11,972	Re: Positive Ground Alternators Hey Chris, welcome to Fordbarn. Personally, if you have had issues jumping a positive ground system, the cause is 'operator error' and really not the fault of the system, but that's ok but just know a positive ground system CAN be successfully boosted off of a negative ground system. If you do decide to reverse the polarity to a negative ground, the only two things that really needs to happen is reverse the polarity on the coil by exchanging the two wires and place them on the opposite respective terminals, and to reverse the wires on the backside of the ammeter. Hopefully your battery cables are long enough to be reversed too, but that should get you to a negative ground. Since the 'one-wire' alternator has an internal self-exciting regulator that always has a current draw on the system, you might consider installing a disconnect switch to interrupt the current when the vehicle is not in use. Another alternative is to install a Model-A generator back on there with a diode equipped cut out and an EVR installed internally where you can eliminate the about half of your headaches and allow the engine compartment to look more aesthetically correct. Again, welcome to the Forum here!! __________________ . BRENT in 10-uh-C . www.model-a-ford.com ...(...Finally Updated!! ) .

07-27-2014, 10:55 AM	#4
Charlie Stephens Senior Member Join Date: May 2010 Location: Southern California Posts: 7,305	Re: Positive Ground Alternators Sponsored Links (Register now to hide all advertisements) I would consider changing the ground over to negative if you have to replace the alternator. Some of the advantages of the 12 volt alternator are lost when you go positive ground such as many of the negative ground alternators are for modern cars and are over the counter at a parts store if you need one on the road and some modern electronics are polarity sensitive which means you should have a negative ground system. Charlie Stephens