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Old 11-17-2008, 12:17 AM   #1
evilways
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Alternator wiring 12si/ EZ wire harness

I have an EZ harness, and a Delco 12si alternator. I am trying to figure out why my battery wonít charge. I just replaced the battery so it is brand new.
I tried the neg post to neg terminal with a light to see if I had a draw on the battery and got nothing.
I hooked up my voltage tester to the battery and started the engine, my volts dropped a couple tenths at idle and then more during engine rev. Is that typical with a dead alternator?
Also to make sure my wiring is correct. I have made a diagram of what my wire hook up is.
Alt. Power-red wire to stud, then jumping to left prong (rear view of alt.
Alt. Excitor-white wire to right prong
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Old 11-17-2008, 02:47 PM   #2
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Re: Alternator wiring 12si/ EZ wire harness

I found the CS130 wire set up with stock harness saying to put the power on the #2 prong, and the Blue wire on the #1.
Is the blue wire the Excitor for that set up? I no longer have the external regulator on mine at all so this is kind of confusing?
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Old 11-17-2008, 05:11 PM   #3
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Re: Alternator wiring 12si/ EZ wire harness

Check this from the FAQS

http://67-72chevytrucks.com/vboard/s...d.php?t=119379

It's important to know if you have a charging light(idiot) or an amp guage.

It appears that you do have the field exciter wire and the sensor wire reversed
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Old 11-17-2008, 11:12 PM   #4
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Re: Alternator wiring 12si/ EZ wire harness

Thanks for the link; I guess I overlooked that one.

I hate the fact the previous owner was the one that put the EZ harness in, even though I have basically rewired most of it. I will try to track down the light wire to make sure my harness is tied in to it.

I think I tried this a while back being confused after moving some wires around, and ended getting a pretty good spark out of the red wire on the #2 prong, I figured that was a bad sign so I put it on the other one and here I am.

Was the spark just it making a connection to the battery then?
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Old 11-17-2008, 11:30 PM   #5
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Re: Alternator wiring 12si/ EZ wire harness

Quote:
Was the spark just it making a connection to the battery then?
I think so since it needs to be coming from a switched on source to avoid draining the
battery overnight. This is pointed out in the following website in item 2.
http://www.6066gmcguy.org/charging.htm
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Old 11-18-2008, 05:15 AM   #6
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Re: Alternator wiring 12si/ EZ wire harness

Ok, I switched the wires on the alt. It is 12.6 at idle 14.5 with low revs so it is charging now, that is good. Turned key off and it shut down properly.

Only thing now, my Gen. light is on? I don't know if the light goes out during high revs, since it's 4am I don't want to wake the neighborhood up, but at idle the Generator light is on, I don't get it, if the alt. is charging shouldn't the light be off?
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Old 11-24-2008, 03:07 AM   #7
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Re: Alternator wiring 12si/ EZ wire harness

I am not familiar with the electrical charging system. So this is what I got so far. I test the battery before start, 12.8volts. I started it and it's at 12.9. When I give it rpms the alternator starts charging and I am at 14.9 at rev and 14.4 at idle. Now as soon as the alternator starts charging my generator light comes on and will not go off, with or without rpms. When I start the engine the generator light will not come on at all until I give it rpms? I thought the generator light was to tell you that youíre not charging? It is charging so I donít get it.

Anyone have ideas to what is wrong?
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Old 11-24-2008, 09:32 AM   #8
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Re: Alternator wiring 12si/ EZ wire harness

My best guess is that the internal regulator in the alternator is bad due to the 12 volts unresisted wire that you had hooked to it before.
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Old 11-24-2008, 10:55 PM   #9
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Re: Alternator wiring 12si/ EZ wire harness

Is the internal regulator a replaceable part on the 12si? Anyone know the part number off hand?

Last edited by evilways; 11-24-2008 at 10:59 PM.
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Old 11-25-2008, 07:12 PM   #10
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Re: Alternator wiring 12si/ EZ wire harness

Yes the regulator is available at most auto parts stores and online. I found the following website and it's possible that your battery voltage is lower than it needs to be for the light to go out. As long as the alternator is charging you might try ignoring the light until the battery gets fully charged. You can't ignore the light wire, because the alternator won't charge without it connected.
Changing the regulator is fairly simple if you go slow and keep track of what you are doing at each step. The regulator is mounted on the rear case of the alternator and when you separate it the brushes will fall out . They fit into two little housings on the back case.I had a step by step teardown saved somewhere and I've been looking for it. If I find it I will post it up.
I don't know if this link will make sense to you but it may help.
http://www.alternatorparts.com/under...lternators.htm
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Old 11-25-2008, 09:22 PM   #11
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Re: Alternator wiring 12si/ EZ wire harness

Ok great, This weekend I will try to let the truck run for a little while to see if the goes out. It is fairly cold out and possibly be taking a minute for the battery to charge full from it sitting in a cold garage.

If that fails I will change the regulator.

I really appreciate your help so far. Not too many people want to aid in electrical problems.
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Old 11-26-2008, 10:28 PM   #12
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Re: Alternator wiring 12si/ EZ wire harness

Here is a rebuilding link from the corvette forum.It is not the one I was looking for but it goes into great detail explaining the alternator. It is in text only but you should be able to follow along.
http://www.lbfun.com/warehouse/tech_...Tech_Paper.pdf
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Old 11-27-2008, 12:16 PM   #13
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Re: Alternator wiring 12si/ EZ wire harness

Thanks that is very helpful; I hope to tackle this on Saturday.
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Old 11-29-2008, 04:29 PM   #14
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Re: Alternator wiring 12si/ EZ wire harness

Ok, I ran the truck for a while and generator light is still on. I took the alternator to my local electrical shop; they seriously doubt it is the alternator faulting? Even though they did not do an internal test on it.

I did a draw test.
With draw (lights on).
14.14v idle
14.23v at rev

No draw
14.34v idle
14.41v rev

I have to order the parts to do the alt. rebuild; do you think I should still go that route?
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Old 11-29-2008, 06:53 PM   #15
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Re: Alternator wiring 12si/ EZ wire harness

I was told that the excitor wire does not need to be connected, since I am using a self exciting alternator. So I tried it and disconnected the excitor wire from the #1 terminal and started the engine. Same result as before, engine start no charge, give it rpms and it charges but without the generator light?

So now, is excitor wire supposed to tell the generator light to come on during an alternator failure?

Or am I getting some kind of resistance from my excitor wire sending a false generator light on?

I cant seem to ever get ahold of EZ wire for questions, I am starting to get frustrated on this issue.
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Old 11-29-2008, 07:23 PM   #16
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Re: Alternator wiring 12si/ EZ wire harness

Well don't I feel like a dumbass now. I had a little light go off in my brain when you said in post 7 that you had 12.2 volts until you reved it and then it was charging.
It appears that you have a one-wire alternator that only requires the large wire off the back to connect to the battery. This is exactly how they are supposed to operate and you will lose the function of the charging light. The regulator in these alternators has a self exciter feature and no wire hookups are needed. Your first post completely threw me off when you had the wires backwards to what they should be for a normal alternator. If you want the charging light to work you will have to change out the regulator in the alternator as that is the only difference in the alternators. You could just get a regulator 12 SI alternator and wire it correctly or you can go with the one-wire and unplug the two small wires. VV
Check out this website---http://www.madelectrical.com/electrical-tech.shtml
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Old 11-29-2008, 07:43 PM   #17
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Re: Alternator wiring 12si/ EZ wire harness

So even if it has the stud on the rear and the two terminal prongs on the side it could still be a one wire alt?
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Old 11-29-2008, 08:21 PM   #18
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Re: Alternator wiring 12si/ EZ wire harness

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Originally Posted by evilways View Post
So even if it has the stud on the rear and the two terminal prongs on the side it could still be a one wire alt?
Yeppers,-----
http://www.classictruckshop.com/one_wire.php
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Old 11-30-2008, 06:37 PM   #19
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Re: Alternator wiring 12si/ EZ wire harness

Excitor-white wire to right prong may need a diode placed in that wire to stop the power from back feeding the light when your shut off.
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Old 12-01-2008, 09:49 AM   #20
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Re: Alternator wiring 12si/ EZ wire harness

subscribed...I'm having the same issues...but I'm using the painless system!
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Old 12-01-2008, 12:15 PM   #21
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Re: Alternator wiring 12si/ EZ wire harness

Quote:
Originally Posted by gcburdic View Post
subscribed...I'm having the same issues...but I'm using the painless system!



Here is the answer to your problem if you are using the painless system. It does not matter what system you use if you have the two small wires reversed then the alternator will backfeed to the fuse block and power the ignition when the key is shutoff.
http://www.painlessperformance.com/M...0501Manual.pdf
Figure 7.2A wire no. 914.

463's post is correct except that he is not clear on which post to run the diode on. Saying "the right side terminal" is deceptive because if you are facing the engine from the front then it is the right side, but as the alternator sits on the engine the correct terminal is the left one or drivers side. not all alternators are numbered but most have the no. one and two on the plug in. No. 1 is the terminal that needs the diode. Also if evil does have a one wire alternator then the diode is irrevalent because no wires connect to the plug.
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Old 12-01-2008, 01:33 PM   #22
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Re: Alternator wiring 12si/ EZ wire harness

VetteVet,

Thanks so much for the info....I actually went to that web site after I posted and re-read that a diode is needed for my problem....so will that take care of the generator dummy light going off too??
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Old 12-01-2008, 05:13 PM   #23
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Re: Alternator wiring 12si/ EZ wire harness

Actually if you noticed on the diagram it says in certain circumstances a diode may be needed. Those circumstances are when you don't have a warning light and have an amp guage type dash, or you just don't have the warning light. If you have the warning light then all you should need to do is to run the brown wire from the light to the no. 1 terminal. In the stock harness the brown wire goes to the old external regulator on the radiator mount next to the horn. The other end of the regulator is either a white or a blue wire and that runs to the alternator no. 1 terminal. Most guys just run the brown wire direct to the new alternator if it's long enough. This is all explained in the FAQ post by Toddtheodd that I referred to in post #3., and again in the link in post 5.
Try this wiring and see if it works and if not we will get back into it.VV
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