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Old 11-06-2019, 04:18 PM
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convert 56 chev. to alternator

Hey you all I am changing my generator out and going with an alternator.
I have heard someone ask if I want a one wire conversion or a two wire?
I would like to keep my idiot lights, so which way and where is the best to
purchase. Thanks . Duane

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Old 11-06-2019, 04:33 PM
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Do NOT get a one wire. There's a reason why GM never installed them in cars from the factory. And the "two wire" is really three. Two in the plug and one heavy wire to the threaded BATT stud.
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Old 11-06-2019, 05:11 PM
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Thanks for reply. This may be a dumb question, but do you know what is the reason for a 2 or 3 wire conversion as apposed to a one? Duane
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Old 11-06-2019, 05:28 PM
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Quote:
Originally Posted by db flyer View Post
Thanks for reply. This may be a dumb question, but do you know what is the reason for a 2 or 3 wire conversion as apposed to a one? Duane
The main wire from the BATT post on the alternator to the junction block is the primary charging wire. The two wire plug on the factory alternators includes a SENSE wire and the FIELD wire that operates the idiot light. The SENSE wire also runs to the junction block and senses voltage there (as opposed to at the alternator) to automatically adjust the voltage regulator output to account for any voltage drop in the wiring. The FIELD wire actually serves two purposes. In addition to operating the idiot light, it also serves to turn on the voltage regulator at low RPMs to ensure the alternator is charging even at idle. Keep in mind that GM cuts every penny possible in building their cars, yet they kept these extra copper wires instead of using a one-wire design. Common sense should tell you that they did this for a reason.

In your case, two of these three wires already exist in the original harness. The heavy charging wire from the generator to the junction block bolts directly to the threaded BATT stud on the new alternator. The brown idiot light wire already runs to the old voltage regulator. Simply connect it instead to the FIELD terminal in the alternator plug. Now run a new wire from the other terminal in the plug to the junction block and you're done. This assumes you are using a 12SI style alternator.

You may want to consider a CS130 instead. I like to use the CS130 from a 1989-1990 Oldsmobile Custom Cruiser with 307 motor. It has 105 amp output, bolts to any 1960s GM alternator bracket, and comes with a V-belt pulley instead of a serpentine pulley. This ACDELCO 3351011 CS130 brand new is under $70 at RockAuto right now. The CS130 uses a four wire plug in addition to the threaded BATT terminal. In that case, simply connect the SENSE wire to the "S" terminal in the plug and the FIELD wire to the "L" terminal (for "light"). Ignore the other two terminals. I've had one of these in my 1962 Olds for nearly ten years now.

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Old 11-07-2019, 06:14 AM
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I would discard the old heavy charging wire and use a AWG8 or AWG6 wire from the Alternator to the Starter motor Battery terminal depending on the alternator output. As the old heavy cable most likely not be able to cope with the increase in amps.

Last edited by brading; 11-07-2019 at 06:40 AM.
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Old 11-07-2019, 09:08 AM
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Quote:
Originally Posted by joe_padavano View Post
The main wire from the BATT post on the alternator to the junction block is the primary charging wire. The two wire plug on the factory alternators includes a SENSE wire and the FIELD wire that operates the idiot light. The SENSE wire also runs to the junction block and senses voltage there (as opposed to at the alternator) to automatically adjust the voltage regulator output to account for any voltage drop in the wiring. The FIELD wire actually serves two purposes. In addition to operating the idiot light, it also serves to turn on the voltage regulator at low RPMs to ensure the alternator is charging even at idle. Keep in mind that GM cuts every penny possible in building their cars, yet they kept these extra copper wires instead of using a one-wire design. Common sense should tell you that they did this for a reason.

In your case, two of these three wires already exist in the original harness. The heavy charging wire from the generator to the junction block bolts directly to the threaded BATT stud on the new alternator. The brown idiot light wire already runs to the old voltage regulator. Simply connect it instead to the FIELD terminal in the alternator plug. Now run a new wire from the other terminal in the plug to the junction block and you're done. This assumes you are using a 12SI style alternator.

You may want to consider a CS130 instead. I like to use the CS130 from a 1989-1990 Oldsmobile Custom Cruiser with 307 motor. It has 105 amp output, bolts to any 1960s GM alternator bracket, and comes with a V-belt pulley instead of a serpentine pulley. This ACDELCO 3351011 CS130 brand new is under $70 at RockAuto right now. The CS130 uses a four wire plug in addition to the threaded BATT terminal. In that case, simply connect the SENSE wire to the "S" terminal in the plug and the FIELD wire to the "L" terminal (for "light"). Ignore the other two terminals. I've had one of these in my 1962 Olds for nearly ten years now.

Thanks for the good info. I will print this out and go shopping. I doubt that I could find a used mounting bracket, but will research to see if some used bracket it the salvage yards may work.
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Old 11-07-2019, 12:18 PM
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What does your generator bracket look like. A picture would be good.
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Old 11-07-2019, 08:36 PM
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X2 on the ditch the old charge wire.



#1 it is not heavy enough.


#2 on a 56 anything, unless that car has been stored in a vacuum, the cotton braid covered rubber insulation is a fire hazard. I would bet that anywhere you move a wire, the insulation will shatter. 50+ years of exposure to the environment would have turned it to carbon.


I have seen mounting brackets cobbled up, do yourself a favor and find some brackets from a 70's era chevy pickup, these will fit the engine and the alternator and save time. They also will secure it properly, for easy belt adjustment and tension stability.


On anything that old I would seriously look at a complete rewire job.
Painless harnesses are a good way to go.


I never trusted Idiot lights for anything, Install a voltmeter not an ammeter.
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Old 12-14-2019, 04:23 PM
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Question about my generator connections ?

I pulled my Generator today but a little confused as to "Juntion block"
My large gen. wire is brown, and goes to the regulator, and a short large red wire from the regulator goes to the horn relay ? Does the horn relay act as the " junction block" some of you members mention ? They are mounted on the drivers fender.
Also I do have a small brown wire running into the dash, which I believe is the idiot light. Thanks.







































'
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Old 12-14-2019, 04:34 PM
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Yes, the center ("B") terminal on the horn relay is the junction block. On later GM horn relays this is actually a threaded post, but in 56 it is just another screw terminal.
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Old 12-14-2019, 05:04 PM
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Ok thanks Joe. Since I'm doing away with the Reg. I will throw away the old large wire from gen. and put on a new heavy wire such as 6 or 8 gauge between the Alt. and horn relay and then follow the other wiring you mentioned.
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Old 12-14-2019, 05:25 PM
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Given the small size of that terminal on the horn relay, you might want to install an aux junction block if you plan to run additional electrical loads like an electric fan, A/C, or electric fuel pump. There are a lot available. GM pickups had one like this under the hood.

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Old 12-16-2019, 11:34 AM
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Unless the old wiring is visably damaged I'd just leave it alone. Messing with te wiring is likely to cause more problems than it solves in that you can get your self into chained replacement leading to most of if not everything not just what your working on. A stock 1956 would still be the era of gross over-engineering and before the finance cost cutters really took over everything in the company. So I would argue for as little intervention as possible, follow Joe's plan its right on getting this done without introducing more effort than necessary.

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Old 12-17-2019, 10:06 PM
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Hey you all I've got dumb question. I installed and wired up my alternator conversion from a generator, and unsure of my wiring even though I wired pretty much as Joe said in his reply to my conversion of my 56 chev. I started her up and my idiot light went out which is a good sign, but without an volt/amp gage, not sure it is charging. I have an old car tester but the alternator tester shows using a shunt bar to test the output of alternator which I`m not familiar with. I could just drive it over to auto parts store, as I don`t want to make a wrong connection with my tester. I would assume my positive tester lead would go to the batt. post on alternator, and my negative lead to a ground, then start car and see if I`m getting a charge on tester. Whaca think ?
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Old 12-18-2019, 03:50 PM
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Quote:
Originally Posted by db flyer View Post
Hey you all I've got dumb question. I installed and wired up my alternator conversion from a generator, and unsure of my wiring even though I wired pretty much as Joe said in his reply to my conversion of my 56 chev. I started her up and my idiot light went out which is a good sign, but without an volt/amp gage, not sure it is charging. I have an old car tester but the alternator tester shows using a shunt bar to test the output of alternator which I`m not familiar with. I could just drive it over to auto parts store, as I don`t want to make a wrong connection with my tester. I would assume my positive tester lead would go to the batt. post on alternator, and my negative lead to a ground, then start car and see if I`m getting a charge on tester. Whaca think ?
I would just use a volt meter. Check voltage across the battery terminals. With the engine off it should be 12.5 or less. With the engine running it should be 13.8 or so if the alternator is charging properly. Don't worry too much about the actual numbers, just note the difference from engine off to engine running.
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