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Old 08-12-2019, 02:05 AM   #1
broberson
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1970 C10 Alternator/wiring issue

So I replaced my alternator because it was magnetized on the front. After replacing it, I added a new 2 wire alternator connector because the old plastic plug was rotted. When I started the truck, the one wire from the plug got really really hot, as did the alternator. Killed the truck, reversed the wires thinking maybe the instructions were incorrect or I had remembered it wrong. After plugging it in, without even starting it, the two wires instantly got hot, so I unplugged it, and went back to the original setup.

I started the truck again a bit later, and the one wire basically melted and the alternator was really hot too. I read that if the battery was low on charge that this would make the alternator run hot, but that isn't the case here, the battery is fully charged. I unplugged the two wire plug from the alternator, and the truck runs great, the alternator stays cool, and no issues there. However, my tach does not work because the wire that is unplugged goes to the ignition. I have pictures of the insturctions attached, so I was hoping for some help here.

The two wires in question are located in circuit branch 8, and is the 4A plug that inserts on the 1 pin behind the alternator (this is the one that melted), and the wire that jumps from the 2 pin to the red power post on the alternator.

My questions are 1. What do the two pins labeled 1 and 2 on the rear of the alternator do? 2. How or where can I place the 4A wire in order to power my ignition/tachometer?

Any help is greatly appreciated. I have three pages attached, the instructions from american autowire 20 circuit harness. The three pages have instructions in the area I am having trouble with.
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Old 08-12-2019, 09:47 PM   #2
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Re: 1970 C10 Alternator/wiring issue

You've got me puzzled about several things. I've never heard of needing to replace an alternator because it was magnetized on the front. What is that like? Was it not working?

Were you replacing the original alternator that requires the external regulator with an internally regulated alternator? Or replacing with another alternator just like the one you removed?

Have you also replaced wiring on the truck?

You also said tach does not work because the wire that is unplugged goes to the ignition. I don't see how the tach could be related to a wire plugged or unplugged at the alternator. You should be able to completely remove the alternator and all connections, and run the truck and everything will work except battery charging. So you really have me puzzled there and I think others may need to help with that one.

It would be good to see some pictures of what you have. Front and back of the old and new alternators and any custom wiring, and what is the wiring like at the regulator, and any jumpers you have at the regulator plug if you use an internally regulated alternator.
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Old 08-12-2019, 10:26 PM   #3
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Thumbs up Re: 1970 C10 Alternator/wiring issue

Whatever you do don't ever run a computer controlled vehicle without the alternator hooked up. The battery will not support it and you run a high risk of burning the Computer up because of low voltage.
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Old 08-12-2019, 11:49 PM   #4
broberson
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Quote:
Originally Posted by dmjlambert View Post
You've got me puzzled about several things. I've never heard of needing to replace an alternator because it was magnetized on the front. What is that like? Was it not working?

-It would actually drain the battery dead. The mechanic advised me that the magnetism was the reason it was bad. So thatís the reason I replaced it.

Were you replacing the original alternator that requires the external regulator with an internally regulated alternator? Or replacing with another alternator just like the one you removed?
Have you also replaced wiring on the truck?
- I rewired the entire truck w the American autowire 20 circuit, and the instructions said I didnít need an external regulator. I bought a remanufactured GM- SI alternator, and I actually donít know if it is internally or externally regulated.

You also said tach does not work because the wire that is unplugged goes to the ignition. I don't see how the tach could be related to a wire plugged or unplugged at the alternator. You should be able to completely remove the alternator and all connections, and run the truck and everything will work except battery charging. So you really have me puzzled there and I think others may need to help with that one.
- The tach is an aftermarket replacement, but itís powered from the 4A wire on the diagram I provided. The truck runs great without the alternator, I just donít have any power to the 4A branch from the alternator..

It would be good to see some pictures of what you have. Front and back of the old and new alternators and any custom wiring, and what is the wiring like at the regulator, and any jumpers you have at the regulator plug if you use an internally regulated alternator.
Iíll take some pictures this weekend and post them
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Old 08-13-2019, 10:12 PM   #5
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Re: 1970 C10 Alternator/wiring issue

After looking at some diagrams on the internet, I've found that the posts on the rear of the alternator are: 1 and 2, or R and F. The 2 post is jumped over to the battery post in the rear, and the 1 post is tied into the "idiot" light or charge indicator, and into the "dash harness brown Alternator Ign exciter connection wire (4A)on the main dash harness" according to the instructions from American Autowire.

The instructions do say that if you are using a one wire alternator, that this wire will not be used, and the only thing tied into the alternator will be on the positive post.

So my question goes back to why is my aftermarket tachometer not working now? It is plugged into the distributor with a plug, but no power I'm assuming because somehow the 4A plug isn't connected to the alternator.. I'm at a loss here..
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Old 08-13-2019, 11:11 PM   #6
dmjlambert
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Re: 1970 C10 Alternator/wiring issue

I don't know. I suggest work on one thing at a time. I don't think the alternator could be related to tachometer, unless you have a computerized truck.

The stock wiring harness has a resistor wire in the cab that goes between the ignition switch and the firewall connector, then from there it is a regular brown wire that connects to the alternator. I don't know if your replacement harness has the same resistance. It probably does.

The wiring harness instructions cannot say that you don't need a regulator, because whether or not you need a regulator depends on whether there is one built into the alternator. The original alternators on these model years of trucks we have did not have a built-in regulator, they depended on an external one. If you know your alternator is an SI series alternator, then that would have a built-in regulator. It may be the type that your new wiring harness is made for.

So what is the more complete picture of what you have going on? Was your truck up and running with the new wiring harness and an SI alternator and everything working for some period of time, and then the battery started getting discharged leading you to put another SI alternator in it and things started going bad from there? Or some other sequence of events? When you went to get the alternator, did you get it from a car parts store and tell them you have a certain make and year of vehicle to get them to hand you an SI alternator instead of giving you the original style alternator for your truck year? Or did you get the alternator from some other source?

I am wondering on a new wiring harness how was the alternator plug already gone bad and needing to be replaced. I am not judging or critical of your story, just trying to get the full picture of what's going on in order to possibly help.

I think maybe the pictures you will take over the weekend may help. If you still have the old alternator that was working before it started draining the battery would be good to see, front and back and connector plug. And the new alternator that is misbehaving, front, back and connector plug, and pictures of your new connector that you attached to replace the bad connector. And whatever wires you have that are now melted.

Sorry to hear about these troubles, I know electrical problems are a drag.
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Old 08-14-2019, 12:49 AM   #7
broberson
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Re: 1970 C10 Alternator/wiring issue

Quote:
Originally Posted by dmjlambert View Post
I don't know. I suggest work on one thing at a time. I don't think the alternator could be related to tachometer, unless you have a computerized truck.

- its stock, no computers in the truck at all

The stock wiring harness has a resistor wire in the cab that goes between the ignition switch and the firewall connector, then from there it is a regular brown wire that connects to the alternator. I don't know if your replacement harness has the same resistance. It probably does.

The wiring harness instructions cannot say that you don't need a regulator, because whether or not you need a regulator depends on whether there is one built into the alternator. The original alternators on these model years of trucks we have did not have a built-in regulator, they depended on an external one. If you know your alternator is an SI series alternator, then that would have a built-in regulator. It may be the type that your new wiring harness is made for.

- Originally I did have an external regulator, but I took that out. Somehow or somewhere, I was put under the impression that with the new harness I didn't have to use the external regulator. That may be the problem, but there isn't anything on the instructions that suggest the use of an external regulator.

So what is the more complete picture of what you have going on? Was your truck up and running with the new wiring harness and an SI alternator and everything working for some period of time, and then the battery started getting discharged leading you to put another SI alternator in it and things started going bad from there?

-That's pretty much what happened. I replaced the harness because under the dash and engine compartment was a mess. Previous owner had spliced into the ignition switch to power a radio, there were blinded wires everywhere, and the rear harness for the brakes/signal lights was rotted.

After I finished installing the new harness, if I left everything connected, the battery would be dead by the morning. I replaced the starter, still had the parasitic drain, then replaced the alternator because of the mechanic suggesting it because of the whole magnetism issue. Didn't get the drain figured out until this past weekend, when everything melted. Once the two wire alternator plug was removed, the drain stopped.


Or some other sequence of events? When you went to get the alternator, did you get it from a car parts store and tell them you have a certain make and year of vehicle to get them to hand you an SI alternator instead of giving you the original style alternator for your truck year? Or did you get the alternator from some other source?

-I got the referb alternator from Oreilly

I am wondering on a new wiring harness how was the alternator plug already gone bad and needing to be replaced. I am not judging or critical of your story, just trying to get the full picture of what's going on in order to possibly help.

- The plug for the alternator was already rotted from the previous owner.

I think maybe the pictures you will take over the weekend may help. If you still have the old alternator that was working before it started draining the battery would be good to see, front and back and connector plug. And the new alternator that is misbehaving, front, back and connector plug, and pictures of your new connector that you attached to replace the bad connector. And whatever wires you have that are now melted.

Sorry to hear about these troubles, I know electrical problems are a drag.
As far as the alternators, they are both the same on the rear, as far as plugs and pins. I have grounded the rear to the heads, along with the battery with a 4 ga wire. I'll get the pics as soon as I can so I can show yall.
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Old 08-22-2019, 03:31 AM   #8
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Re: 1970 C10 Alternator/wiring issue

After talking to a rep from American Autowire, he informed me that this was a universal harness and does not have a specific charge indicator circuit, and that he also does not know how it is affecting the power to the tach, because the tach gets its signal from the white tach wire and power from the pink circuit 39 in the instrument cluster on circuit branch 7.

So now that the heating up/melting issue has been figured out, where would a suitable point be to connect the charge indicator wire that I had initially plugged into the rear of the alternator? Could I simply wire a ring connector and put it on the red post with the power to the alternator? I'm so confused!!
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Old 08-25-2019, 05:23 AM   #9
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Re: 1970 C10 Alternator/wiring issue

The diagram in your instructions that came with the new wiring harness is rather "flaky".. First, you need a factory wiring diagram pertaining to your truck and a factory diagram for a later model having an internal regulator.. Compare the two and you will understand the wiring modifications needed.. Take a look at this thread, post #2. http://67-72chevytrucks.com/vboard/s...ire+alternator It's for a dash that has am ammeter, not a light.. Search this site for a wiring diagram for a charge light if that's what you have..
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Old 08-25-2019, 02:30 PM   #10
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Re: 1970 C10 Alternator/wiring issue

This thread should answer all your questions about converting to an internally regulated alternator.

http://67-72chevytrucks.com/vboard/s...d.php?t=763180
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Old 08-25-2019, 02:49 PM   #11
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Re: 1970 C10 Alternator/wiring issue

Here's one that might be even better.
http://67-72chevytrucks.com/vboard/s...d.php?t=417872
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