Short to ground in my alternator?

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like_A_pike

like_A_pike

that's not factory
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1968 Barracuda originally a 318 automatic now 340 with a chrome box, no additional electronics.

The horn relay burned up not long after I replaced the turn signal switch. I think I chased that down to where I pinched the wire harness between the dash and the steering column supports.
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I think I have that sorted but I am still getting 12.35v to my multimeter between the block and the negative battery terminal.
I have a fuse in the fusible link that I remove and replace between tests. Those tests have led me to the alternator. The wire to it checks out ok. I get the 12v at the ground when I reconnect the alternator.
My question are; do I understand correctly that I should not be getting 12v at the ground with that connected (I assume properly. It’s a square back Powermaster. It’s been in there for a few years without issues) and can I open the alternator up, find and fix the short or is it toast?
 
Can you be more specific on how you are testing, or what you are testing?
When you say block, is that referring to the engine block? Are the battery cables connected to the battery or do you have one off?
 
Sure. I removed the negative terminal from the engine block and connected the ground multimeter lead to it. When I touch the block with the positive lead, I get 12.35v. With the fuse in the fusible link AND the alternator connected. Remove just the alternator and I get 0.3v. Remove the fuse and I get nothing.
 
I think you are testing wrong. Reconnect everything and test for voltage on a complete circuit.

Your tests are not showing anything wrong with your alternator.
 
I found this.
www.forabodiesonly.com

one wire Alternator and voltage regulator question

Please help me understand how this works. The replacement alternator I got has the square back and the directions say to not use my voltage regulator (VR). Does the regulator do anything other than protect the battery from overcharging? How does the one wire or "squareback" alternator do that...
www.forabodiesonly.com www.forabodiesonly.com

So at this point (we on this side of the screen) can't assume anything.

As far as the alternator alone goes.
Diconnect the battery and alternator. if there is just one terminal (stud) check for resistance to ground. Should be infinate.
If there is are two field wire connections. The resistance to ground should be infinate.
if one of the field wire connections is grounded, disconnect the ground wire or remove the brush - which ever is appropriate.
 
Am I doing that correctly? Should I remove this?…

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Edit: Got the same reading either way
 
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Could be short. But a short should have blown the fusible link or fuse - not sure how its wired now.
Could be blown out diode(s). Try it on the low scale 200.
Touch the probes together to find out the what the meter is calling zero.
Use the alternator's housing or attaching hardware as the ground reference.


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These are both field terminals.
Each one is connected to a spring loaded carbon brush and held in place with the screw.
They are insulated from the housing BUT
But I don't know what Powermaster did to that alternator. They may have grounded one.
And the green wire connects to what?

Here's an example of a revised squareback brush and terminal assembly that was grounded with a metal washer.
Originally the revised squareback was an isolated field alternator and insulating washers were used.
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Well there was “an event”! It blew a 20A fuse, both brake light bulbs, and my ballast resistor a couple drives ago.
That led me to chase down that horn short once and for all. Even took out the front seat and prepared for a fight! Replaced the bulbs, resistor, and up’d the amperage of that fuse to 30. But still get sparks when I replaced the negative battery terminal?? Now I’m at the far end of my fusible link. Thinking I’ve found my smoked gun!
So I get “overloaded” until I crank the meter up to at least 20k. 19+ on that scale, and can replicate it on any ground AND the alternator body…
 
The multimeter shows 0 on every range except 200 or 200M when the leads are x’d. I get 00.1 or 00.9 respectively.
 
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If that is one of the non conducive washers, then…

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Would you reckon that little plastic collar under there would also be there to keep the field from contacting the body? I can’t tell if it’s melted or broken but it seems some of it is missing.
Are y’all aware of where one might find a new one?
 
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