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Don't have another top post but it is on a charger right now, I have looked at and watched conversions to 1 wire alt hookups for Chevys. can't help but think this one as done wrong. not shows a wire going from the alt straight to the battery.
If you don't have the correct alt you can't just hook it up with one wire to the batt. This is where the test meter will help determine if your alt is creating an output. But first, you need to figure out why the engine won't turn over.

What do the headlights do when you turn them on?

Get us some pictures of what you have for an alt, external regulator and wiring. From there I or we can help with a plan.

All the power for the ignition and headlights comes in through a black wire running from the horn relay through a fusible link then the wire turns orange and feeds the rest of the cab. The fusible link may be bad. You need to see if you have power at the orange wire near the fusible link. If so, check for power at the fuse box.
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I'll be back in the am. gotta go.
 

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After you get it charged why not take it to an auto parts and have it tested. Then you can illiminate one major item.
For what it worth i have had two year old batteries fail in my Chevelle. So not very old is relative. I have also had batteries that lasted 8 years. So you never know.
 
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Hello everyone, Just got the dirt from the auto parts store. The battery would charge for them also but it would show a voltage drop soon after. buy the time i got there it had gone from 12.6 down to 8.1!Now it is down to 6.6 You guys are right. still concerned with the way it was wired though and if I should go back to original alt setup. alt wires are intact and would just need another alt,battery and some time. Or, if one of you have done the conversion could you tell me what alt to get and the correct way to wire it. Many thanks to all who responded,let me know what you think my next step should be,Dave
 

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Hello everyone, Just got the dirt from the auto parts store. The battery would charge for them also but it would show a voltage drop soon after. buy the time i got there it had gone from 12.6 down to 8.1!Now it is down to 6.6 You guys are right. still concerned with the way it was wired though and if I should go back to original alt setup. alt wires are intact and would just need another alt,battery and some time. Or, if one of you have done the conversion could you tell me what alt to get and the correct way to wire it. Many thanks to all who responded,let me know what you think my next step should be,Dave
If after having a new battery your car doesn't start, the cause may be the purple wire going between the starter and the neutral safety switch, this is a common problem due to a bad connection at the bulkhead connector at the firewall. Sometimes this problem also has to do with a misadjusted parking switch at the steering column. This switch goes on the upper side of the steering column under the dash and is activated by a long rod wich is also connected to the black collar that goes in the column between the column key and the cluster. Try moving this collar a little and perhaps the car may start.

Some years ago, the purple cable that goes to the starter went loose and I ended checking up to the fuel tank before noticing it! Plugged it and the engine started.
 

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Thanks, going to try covering all the bases. I have had several Chevelle's/ElCamino's thru the years but this issue has had me stumped.With help from everyone I think I'am on the right path.
 

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Next move would be the following. Get a multimeter and select the DC voltage. Start the engine and place the black lead of the meter on the battery negative post and the red lead on the positive battery post. Your meter should read between 13.5 - 14.5 volts. If so then your alternator is operating correctly.
 

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previous owner attempted 1 wire alt set up and was done incorrectly.
If that is a one wire alternator then it should not be wired to an external voltage regulator. AFAIK one wire alternators have an internal voltage regulator. Show a pic of the plug on the alt and the connector.
 

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If that is a one wire alternator then it should not be wired to an external voltage regulator. AFAIK one wire alternators have an internal voltage regulator. Show a pic of the plug on the alt and the connector.
Nothing was connected. Did you see the diagram I posted of how it was wired by the previous owner? I'am thinking I should get a correct alt and wire it the way it was from the factory. Could this have caused a overcharging problem? Cooked the battery?
 

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It seems you have no confidence in a one wire alt so why not scrap it and install a regularly wired alternator ? 1 wire alt's are usually reserved for race cars or Hi-performance type cars.I would also suggest when you install the new alternator you install one with an internal voltage regulator or at the least an optional 65 amp alt.
Plus that battery voltage dropping like that means its done,a healthy battery will hold its voltage till you use it.When you buy a new battery get the best one you can afford.
 

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Ok, this is what i would do. Looks to me that the alternator that you have may be a 12 SI type. I ran that number (17294) and it comes up for a powermaster 12SI. I think the 190505 may be the date code. I think the externally regulated alternators have prongs that run opposite of the prongs on your alternator. If it is then that is an internally regulated alternator and your wiring is incorrect.
Here is a tech thread on how to wire correctly for an internally regulated alternator.

https://www.chevelles.com/techref/ftecref14.html
 
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I'am sure 1 wire is a good way to go,My concern is the way it was set up by the previous owner and if that caused the battery failure. this is the way it wired.
 

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Ok, this is what i would do. Looks to me that the alternator that you have may be a 12 SI type. I ran that number (17294) and it comes up for a powermaster 12SI. I think the 190505 may be the date code. I think the externally regulated alternators have prongs that run opposite of the prongs on your alternator. If it is then that is an internally regulated alternator and your wiring is incorrect.
Here is a tech thread on how to wire correctly for an internally regulated alternator.

https://www.chevelles.com/techref/ftecref14.html
This is your instructions for the alternator you have.
https://static.speedwaymotors.com/pdf/7294_instructions.pdf

It needs to be wired as below.

All the above info is correct.

You have a 100 amp 12si Powermaster alternator. The 12si alt is a good upgrade to the stock alt. With the PW alt, you have a few choices of how to wire the system. One wire is basic and good for farm tractors without a bunch of accessories. The 3 wire system is usually the best system to use with the stock wiring harness. If you pull a lot of accessory power off the battery, then a 3 wire system that senses directly from the battery is a better way to go in some applications.

The PM 12si will function either with only one wire connected or with the stock wiring circuit upgraded as in the Oldcutlass's link. As a one wire alt, it will read and adjust the output off the charge terminal on the back of the alt. The alt will be turned on and off by an internal circuit in the alt. Not all 12si alts have this circuit, so if you don't get a charge, you need to hook up as per the link. Term 1` will supply and control the on/off circuit. Without the 1 and 2 terms connected you lose function of the alt warning light in the dash. So you lose the heads up given when your charge system fails, or when the water pump belt fails. Another issue that sometimes arises is that the internal circuit will require a bump in the throttle to 1400 rpm to turn on the alt to begin charging. Once on, it will stay on until the alt stops spinning.

One negative of the one wire system on a stock wiring harness is that it does not compensate for voltage drop where it will do the most good. This can lead to lower running voltages to ignition and headlight circuits. The stock retrofitted 3 wire system is a better way to go as it senses the voltage at a point away from the battery and compensates for common voltage drop in the system. The sense wire reads from the 4 way splice near the horn relay instead of sat the alt or battery.

(Do Not disconnect the battery while the engine is running!) Doing this will damage the alt/regulator.

If that's confusing, please read the following links and they should get you up to speed. This will help you determine the best system for your application. Even though the link is listed as "catalog"' each link covers a different aspect. At the very least just read through them and you'll gain the knowledge to best suit your needs.

Did you ever buy that volt/ohm meter? You'll need one and it will make your job much easier instead of just guessing what's going on. Plus the results will help us help you should you need the help. Without it, we're all just giving our best guess.

https://www.powermastermotorsports.com/faq-alternators_a.html#1 How do I hook up a one wire alternator? When to use a one wire alternator?

Catalog CHEVY MAIN ELECTRICAL POWER-UP SYSTEM

Catalog For most applications, the advantages of a THREE-WIRE alternator will far outweigh the little time saved with a ONE-WIRE installation

Catalog REMOTE VOLTAGE-SENSING IS THE KEY TO GOOD ELECTRICAL SYSTEM PERFORMANCE…

Catalog ALTERNATOR WIRING KIT for the GM DELCO“SI” series alternators

Your battery voltage without the engine running should be about `12.6 volts. With the engine running you should see about 13.8 volts. If you don't see a rise in voltage after the engine has been running for a few minutes, blip the throttle up to 1400 rpm. If you still don't see the 13.8, then your alt is not charging. you have electrical issues or the alt/regulator is caput. If you see over 14.5 volts, you regulator is bad and you are over charging. This will lead to a cooked and damaged basttery in short time.
 
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