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Old 10-22-2007, 11:32 AM   #1
rab71
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Default GM 10si (3 wire)alternator question

What happens if I don't hook up the wire that is supposed to go to the idiot light? Will the alternator not charge? I don't have an idiot light in my truck. So can I just hook it to a gauge light or something? If that is the case then Ijust hook it to the positive side of the light, and the negative just goes to ground, correct? It will light if the alternator stops charging then?

Or can I hook it to an ammeter that shows positive or negative charge?

Thanks
Rob
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Old 10-22-2007, 11:36 AM   #2
36-3window
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Default Re: GM 10si (3 wire)alternator question

that wire excites the alternator so it will charge...just hook it to 12 volt SWITCHED power

wiring an ammeter is a whole different thing
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Old 10-22-2007, 11:41 AM   #3
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Default Re: GM 10si (3 wire)alternator question

I don't mean to hijack the thread but can you make a diagram or have photos? I have the same problem on my 64 chevy pick 'em up...so yeah the alt won't charge at all with out some sort of wire mods

Mike
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Old 10-22-2007, 11:43 AM   #4
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Default Re: GM 10si (3 wire)alternator question

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Old 10-22-2007, 11:44 AM   #5
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Default Re: GM 10si (3 wire)alternator question

This site has a lot of info on alternators etc. -

http://www.madelectrical.com/index.shtml
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Old 10-22-2007, 11:58 AM   #6
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Default Re: GM 10si (3 wire)alternator question

Thanks guys I think I found my answer to the ammeter question too.

http://shiftworks.com/flash/amp-gauge.swf
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Old 10-22-2007, 12:01 PM   #7
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Default Re: GM 10si (3 wire)alternator question

SO actually I just run the whit wire n the drawing to the ignition switch, so when it is in the ON (not start) position it gives the #1 wire juice?
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Old 10-22-2007, 12:45 PM   #8
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Default Re: GM 10si (3 wire)alternator question

If I can I will try to help a little. An idiot light needs to be a two wire light. That means it can't use the housing or base as the ground. One of the two wires on a two wire light needs to run to a switched( you only want the light to come on with the ignition switch) voltage source. The other wire runs to the Alternator.
How it works is when the Alt. is not running it allows the current from the light to go to ground ,the light will light because the Ign. switch is putting power into the light and the alternator is making the ground. The instant the Alt. starts charging the ground is no longer available so the light goes off because it now has TWO hot wires and no ground.
Hope this helps.
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Old 10-22-2007, 03:18 PM   #9
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Default Re: GM 10si (3 wire)alternator question

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Sweet that helps me out too!!

Thanks,
Mike
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Old 10-22-2007, 03:24 PM   #10
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Default Re: GM 10si (3 wire)alternator question

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This site has a lot of info on alternators etc. -

http://www.madelectrical.com/index.shtml
love that place. breaks it down so I can understand.
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Old 10-22-2007, 03:36 PM   #11
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Default Re: GM 10si (3 wire)alternator question

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One of the two wires on a two wire light needs to run to a switched( you only want the light to come on with the ignition switch) voltage source. The other wire runs to the Alternator
I get it... The #1 wire acts as a ground if the alternator stops charging. That is why when you are starting the car the idiot light is usually on. (Ever so briefly.) Thanks guys!
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Old 10-22-2007, 04:51 PM   #12
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Default Re: GM 10si (3 wire)alternator question

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Originally Posted by 36-3window View Post
You do need to have an indicator lamp (or a diode) connected to the end of that white wire, then to the switched power. If you connect it directly to switched power (the ignition side of the switch) you're gonna have to either use the choke to kill the engine, or stall it in gear, 'cause you won't be able to turn it off with the ignition switch. Once that alternator starts to charge, there's voltage on that white wire, and if it's connected directly to the ignition switch then it's also connected to the coil, right? By using an indicator lamp, you've got enough resistance in the circuit so that it won't allow enough current to flow for the coil to fire.
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Old 10-22-2007, 05:15 PM   #13
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Default Re: GM 10si (3 wire)alternator question

Is it a diode or a 10 Ohm resistor? Why is this so hard for me? Really It should be simple... I think I am just going to go to the junk yard tear out an indicator light...
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Old 10-22-2007, 08:11 PM   #14
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Default Re: GM 10si (3 wire)alternator question

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Is it a diode or a 10 Ohm resistor? Why is this so hard for me? Really It should be simple... I think I am just going to go to the junk yard tear out an indicator light...

I suppose a resistor would work, and 10 Ohms would probably be OK. I would think 10 Ohms would be enough to limit the current to below what would saturate the coil. But I like to use a light, as it's a handy indicator that the system is working.
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Old 10-22-2007, 08:44 PM   #15
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Default Re: GM 10si (3 wire)alternator question

yes to what is said above. only thing i would add is, i think it's a good idea to have some warning if the alt dies. i got these little lights from pep boys for $4, they are domed, have a brushed ring and look old.
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Old 10-23-2007, 11:56 AM   #16
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Default Re: GM 10si (3 wire)alternator question

Since the wire from the alternator needed to be hooked to a switched source that did not interfere with the ignition system I hooked it to my electric fan. I then also hooked it to the ammeter. This actually works as the alternator is charging and the ammeter is reading amperage. Although I think I am going to change it because I really like the way those little lights look on the dash.

Thanks!
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Old 03-06-2008, 09:42 PM   #17
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Default Re: GM 10si (3 wire)alternator question

Good stuff to look at again
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Old 03-07-2008, 08:22 AM   #18
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Default Re: GM 10si (3 wire)alternator question

OK be cautious about hooking power directly to an electric fan. It should always be relayed. The problem you can have is if you are motoring down the road and you have to shut the motor off there is a good chance it won't die. The air moving past the fan keeps it spinning and it will produce enough current to allow the car to continue running. We had this problem with a drag car and when we clicked it off on coast down the car would continue to run until the car stopped.
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Old 03-07-2008, 10:31 AM   #19
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Default Re: GM 10si (3 wire)alternator question

I've been running these alts for years in a bunch of cars and have never run that wire? and i've never had a problem with my alt or battery?
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Old 03-07-2008, 10:42 AM   #20
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Default Re: GM 10si (3 wire)alternator question

Run the diode or run the white wire to the accessory side of the switch.

Primed 55 I think the old saying was that if you revved the motor quick after you started it, it would energize the alternator without the white wire hooked up.
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Old 03-07-2008, 10:51 AM   #21
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Talking Re: GM 10si (3 wire)alternator question

A couple of things you need to know:

1) If you use a 10 ohm resistor, it is going to be at least 15 watts. Using Ohm's laws I= E/R so if E = 12V and R = 10, then I (Amps) = 1.2 amp. Next take P (watts) = E x I, so 12V x 1.2amp = 14.4 Watts. As I said resistor will be more than 15 watts (huge in size). ( I would just put a lamp somewhere not seen)

2) By hooking the white terminal to the ACSY (accessory) terminal of the ignition switch should work also, since when the ignition switch is off, so is the ACSY terminal. (I would still put the resistor or lamp in series with this terminal.

Last edited by d2_willys; 03-07-2008 at 11:00 AM.
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Old 03-07-2008, 11:18 AM   #22
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Default Re: GM 10si (3 wire)alternator question

So... if the lamp burns out does the alternator stop charging?
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Old 03-07-2008, 11:51 AM   #23
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Default Re: GM 10si (3 wire)alternator question

good question, I will check my manual, even though the Buick shop manuals are wrong as far as internal diagram of the built in regulator. Seems they forgot to draw in another transistor. Too complicated to get into on hamb.
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Old 03-07-2008, 12:42 PM   #24
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Default Re: GM 10si (3 wire)alternator question

That takes care of two wires now what abou that pesky 3rd wire, the blue one that is supposed to be sense remote voltage to tickle the internal regulator. What is that hooked to and can the amp gauge be placed in that circuit? In my Studebaker truck there is a 20 or thirty amp breaker behind the instruments. This functions as the "fuse panel" for evrything but lighting. I was thinking that the blue wire could go on the load side of the breaker. Since voltage being used would be pasing through there, is this a good place for this wire?
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Old 03-07-2008, 01:50 PM   #25
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Unhappy Re: GM 10si (3 wire)alternator question

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Originally Posted by plym_46 View Post
That takes care of two wires now what abou that pesky 3rd wire, the blue one that is supposed to be sense remote voltage to tickle the internal regulator. What is that hooked to and can the amp gauge be placed in that circuit? In my Studebaker truck there is a 20 or thirty amp breaker behind the instruments. This functions as the "fuse panel" for evrything but lighting. I was thinking that the blue wire could go on the load side of the breaker. Since voltage being used would be pasing through there, is this a good place for this wire?
ok, here goes:

first, in my previous post I explained that the 10 ohm resistor would have to be 15 watts. This is not true upon further examination, it can be a small 10 ohm resistor, since the internal voltage regulator takes care of the field being energized via a transistor arrangement.

second, there are two ways of hooking up terminal #1 (field exciter). You can use the 10 ohm resistor or the lamp and connect it between the #1 and Acsy of the ignition switch. Yes, if the bulb burns out, no charging results, same for resistor.

third, #2 terminal (sense) should be connected to the battery directly. You could just connect to big terminal on alternator or bring it up to the + of battery (my preference).

fourth, to hook an ammeter up, find where the + large cable from battery goes and then find the other wires going to same terminal (usually solenoid). Remove the smaller wires leaving the big cable connected. Then connect the ammeter with one terminal to the big cable connection (+ of ammeter) and the other to the smaller wires originally connected to the big cable. IMPORTANT: USE #10 STRANDED WIRE FOR AMMETER CONNECTIONS

lastly, if the sense wire is left unconnected it will allow the alternator to overcharge the battery so hook it up!

Good luck
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Old 03-07-2008, 04:38 PM   #26
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Default Re: GM 10si (3 wire)alternator question

It's nice to see this brought back. I did resolve my issue by using the ammeter. I have been driving the truck ever since with no problems. As for the electric fan, I have run direct voltage to them many times w/out a problem but my luck that will change so I will probably add a relay shortly. The white wire that you speak of being off the truck just would not charge. Maybe I have something else funky I dunno'. But it is working well and to me that is what matters. Thanks again guys.

Rob
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Old 03-07-2008, 06:07 PM   #27
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Default Re: GM 10si (3 wire)alternator question

All cars are different. On the 5-6-7 chevy's sometimes we have no problems with them not turning off. Using the big alts seems to over ride the old style switches and fuse boxes. i think you should use the diode and let it work like a one way valve to help kill the power when you turn off the engine. One of the after market A/C compaines have had a problem for years of the engine not turning off if you did so with the fan switch on. The a/c lets the power feed back to the alt. The diode stops that.
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Old 03-07-2008, 06:59 PM   #28
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Default Re: GM 10si (3 wire)alternator question

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So... if the lamp burns out does the alternator stop charging?
first year cadillac sevilles had a charging problem when the alternator light burned out.
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Old 03-07-2008, 09:21 PM   #29
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Default Re: GM 10si (3 wire)alternator question

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So... if the lamp burns out does the alternator stop charging?
yes

ok here another question.......is there anyway to hook-up a warning light on a single wire gm alt (converted 10si).
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Old 03-07-2008, 09:36 PM   #30
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Default Re: GM 10si (3 wire)alternator question

I have always done this using the DIODE. A 12 volt (or higher) 1 amp diode works with "normal" 10si - a HIGH output alt will require a higher amperage rating - jump to a 5 amp in that case. Never had any electric fan issues (keeping the car from shutting off) or had any "slow drains" killing the battery. I know other guys have had sucess with other methods, but I've heard others having issues as well - never heard or had any issues (yet) running the diode.
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