The Ford Barn

rcrra · 07-23-2016, 09:19 AM

Completing a total rebuild on 30 A coupe. All new wiring and conversion to
12 volt with a one-wire alternator. Just added gas and tried to start for the
first time since tear-down. Wouldn't hit a lick. Found the fuse blown at the
starter. Replaced fuse and after turning on the disconnect switch( on the
grounded side) the fuse was blown again. After going over the wiring it seems
to go back to the alternator. This is a new alternator purchased from Mac's if
I remember correctly. Looking at the back of the alternator with it installed on
the top right is the main connect terminal for the battery, horn and lights. On
the left is two terminals with a metal connection between to two of them. Is
this correct or should the metal connector be removed. I may be totally wrong
and the problem be something simple somewhere else in the wiring, but thought
you guys might have some suggestion. Sure would appreciate your thoughts
as I am sort of floundering around now.

Y-Blockhead · 07-23-2016, 10:06 AM

Can you disconnect the alternator and see if the fuse still blows? Then determine if it's the alternator or something else.

I once had a short in one of my headlight buckets. When I would connect the wire to the alternator it would blow the fuse. After I corrected the problem I added a 20a circuit breaker between the alternator and headlight switch (hidden in the frame rail).

I use a 30a circuit breaker in the main fuse holder (at the starter).

rcrra · 07-23-2016, 10:21 AM

Thanks Y, I'll try that.

Tom Wesenberg · 07-23-2016, 11:01 AM

Make sure the alternator voltage and polarity match what you have for the battery. I'm thinking it might be set up opposite polarity.

Instead of blowing fuses, just use a short wire and give the fuse holder contacts a quick strike to see if it sparks. No spark with everything connected, then go ahead and install the fuse.

tbirdtbird · 07-23-2016, 02:32 PM

pic of 'metal connector' please
sounds like the 1 and 2 terminals are bonded for some reason. These are not used with a one-wire setup

rcrra · 07-23-2016, 06:54 PM

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I am rapidly becoming stumped and bewildered. I removed the metal connector tbird and it had no effect. Tom, when I ordered the alternator it was supposed to be one for a 12v
system with a negative ground. By using a wire to check across the fuse block I find what
seems to be a direct short. It really sparks. This is with the key off. I have rechecked the
terminal box to generator harness and the instrument panel harness. It all seems to be wired correctly. I've checked each wire to make sure it is not shorted on the body. I've
checked the terminal box lugs to make sure they are not grounded and found they are ok. This may be a dumb question, but when converting to a negative ground system do
you have to change any of the above wiring harness positions? I am not going to give up, but am perplexed at this point.

Mitch//pa · 07-23-2016, 07:02 PM

Start disconnecting individual circuits until you isolate the short.. I would do that at the junction box

Bob C · 07-23-2016, 07:20 PM

Do like Mitch says, I would remove the three wires (horn, lights and battery)
from the alt and see what happens.

Bob

Mike V. Florida · 07-23-2016, 10:43 PM

Quote:

Originally Posted by rcrra

This may be a dumb question, but when converting to a negative ground system do you have to change any of the above wiring harness positions?

Nope, when changing from pos to neg the coil wires and the ammeter wires are the only things changed.

Here are the instructions that come with the MAC alternator.

http://www.macsautoparts.com/assets/.../A10000A12.pdf

rcrra · 07-25-2016, 11:31 AM

Just as I suspected it was something simple that I was overlooking. With a little prodding
from you guys I went back to the horn/light circuits. I removed them, put the battery wire
back on the alternator and Shazam! No more short. I was almost sure I had checked them
before, but now stand corrected. Thanks so much for the comments.

Tom Wesenberg · 07-25-2016, 06:28 PM

When there's a short in the car that's where I like to start, (at the cutout). I remove the wire that feeds the terminal box and the lights/horn wire, then see if there is a short. If no short, then I touch the power wire to the cutout terminal to see if it sparks. No spark, then move the power wire over to the lights wire.

By just removing this one cutout screw, you can divide the short to 3 places, 1) before the generator and lights, 2) at the generator and cutout, or 3) at the lights and horn circuit.

For shorts, it's DIVIDE and CONQUER.

07-23-2016, 09:19 AM	#1
rcrra Junior Member Join Date: Jun 2012 Location: Oklahoma Posts: 17	Is it my alternator or not Completing a total rebuild on 30 A coupe. All new wiring and conversion to 12 volt with a one-wire alternator. Just added gas and tried to start for the first time since tear-down. Wouldn't hit a lick. Found the fuse blown at the starter. Replaced fuse and after turning on the disconnect switch( on the grounded side) the fuse was blown again. After going over the wiring it seems to go back to the alternator. This is a new alternator purchased from Mac's if I remember correctly. Looking at the back of the alternator with it installed on the top right is the main connect terminal for the battery, horn and lights. On the left is two terminals with a metal connection between to two of them. Is this correct or should the metal connector be removed. I may be totally wrong and the problem be something simple somewhere else in the wiring, but thought you guys might have some suggestion. Sure would appreciate your thoughts as I am sort of floundering around now.

07-23-2016, 10:06 AM	#2
Y-Blockhead Senior Member Join Date: Jul 2011 Location: Redondo Beach, CA Posts: 5,849	Re: Is it my alternator or not Can you disconnect the alternator and see if the fuse still blows? Then determine if it's the alternator or something else. I once had a short in one of my headlight buckets. When I would connect the wire to the alternator it would blow the fuse. After I corrected the problem I added a 20a circuit breaker between the alternator and headlight switch (hidden in the frame rail). I use a 30a circuit breaker in the main fuse holder (at the starter). Last edited by Y-Blockhead; 07-23-2016 at 10:15 AM.

07-23-2016, 10:21 AM	#3
rcrra Junior Member Join Date: Jun 2012 Location: Oklahoma Posts: 17	Re: Is it my alternator or not Thanks Y, I'll try that.

07-23-2016, 11:01 AM	#4
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Is it my alternator or not Make sure the alternator voltage and polarity match what you have for the battery. I'm thinking it might be set up opposite polarity. Instead of blowing fuses, just use a short wire and give the fuse holder contacts a quick strike to see if it sparks. No spark with everything connected, then go ahead and install the fuse.

07-23-2016, 02:32 PM	#5
tbirdtbird BANNED Join Date: May 2012 Location: inside your RAM Posts: 3,134	Re: Is it my alternator or not pic of 'metal connector' please sounds like the 1 and 2 terminals are bonded for some reason. These are not used with a one-wire setup __________________ '31 180A

07-23-2016, 06:54 PM	#6
rcrra Junior Member Join Date: Jun 2012 Location: Oklahoma Posts: 17	Re: Is it my alternator or not Sponsored Links (Register now to hide all advertisements) I am rapidly becoming stumped and bewildered. I removed the metal connector tbird and it had no effect. Tom, when I ordered the alternator it was supposed to be one for a 12v system with a negative ground. By using a wire to check across the fuse block I find what seems to be a direct short. It really sparks. This is with the key off. I have rechecked the terminal box to generator harness and the instrument panel harness. It all seems to be wired correctly. I've checked each wire to make sure it is not shorted on the body. I've checked the terminal box lugs to make sure they are not grounded and found they are ok. This may be a dumb question, but when converting to a negative ground system do you have to change any of the above wiring harness positions? I am not going to give up, but am perplexed at this point.

07-23-2016, 07:02 PM	#7
Mitch//pa BANNED Join Date: May 2010 Location: Bucks County, PA Posts: 11,454	Re: Is it my alternator or not Start disconnecting individual circuits until you isolate the short.. I would do that at the junction box

07-23-2016, 07:20 PM	#8
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,754	Re: Is it my alternator or not Do like Mitch says, I would remove the three wires (horn, lights and battery) from the alt and see what happens. Bob

07-25-2016, 11:31 AM	#10
rcrra Junior Member Join Date: Jun 2012 Location: Oklahoma Posts: 17	Re: Is it my alternator or not Just as I suspected it was something simple that I was overlooking. With a little prodding from you guys I went back to the horn/light circuits. I removed them, put the battery wire back on the alternator and Shazam! No more short. I was almost sure I had checked them before, but now stand corrected. Thanks so much for the comments.

07-25-2016, 06:28 PM	#11
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Is it my alternator or not When there's a short in the car that's where I like to start, (at the cutout). I remove the wire that feeds the terminal box and the lights/horn wire, then see if there is a short. If no short, then I touch the power wire to the cutout terminal to see if it sparks. No spark, then move the power wire over to the lights wire. By just removing this one cutout screw, you can divide the short to 3 places, 1) before the generator and lights, 2) at the generator and cutout, or 3) at the lights and horn circuit. For shorts, it's DIVIDE and CONQUER.