Quick 12si alternator question

[Mr Nick]

Hoooking up a 94 amp 12si alt in my 69 Cutlass. I'm using a volt gauge, and I don't care about the charge warning light on the dash.

I've eliminated the factory wiring for the charging system, re-wiring it with aftermarket wires and connections.

Can I simply leave the #1 terminal on the alternator disconnected?



I will still use #2 terminal for remote voltage sensing at my junction block.

Will I have any problems/issues by basically using it as a '2-wire' alternator?

Thanks,
Nick

[MonzaRacer]

if you look at after market plugs and some cars the big guage wire is ran to the battery post on the back of the alternator and the little one is 12 volts key on but it can be in same cicuit as the igniton.
The trick is to jump the wire (if using stock external wiring )thats 12 volts key on and simply trace the wire from the old regualtor harness(i build about 50 dummy regulators a year with jumpers in them) and connect them .Or you can simply extend that wire to the alt too. or pick one of the 12 volt key on in fuse box but if car doesnt shut off with key then you need to choose a different one.

[Mr Nick]

I don't have any of the original wire harness for the charging system. It was some what hacked up by the previous owner, and I just took it all out. Right now I have 8 gauge cable from alt output to horn relay, and another 8 gauge from horn relay to batt +. I also have small accessories hooked up at the horn relay.

I currently have the #2 terminal (sense wire) going to the horn relay as well, so all my accessories hooked up there get 14.2 volts.

So, terminal #1 NEEDS to be hooked up to a Key On source in order for the alternator to function properly?

[6'9"Witha69]

So, terminal #1 NEEDS to be hooked up to a Key On source in order for the alternator to function properly?

Yes. The alternator needs to be turned on. If you have an MSD then this is the wire you will need a diode on. If needed I can look at my MAD electrical diagram again.

[MonzaRacer]

I had to go get an old alt and a plug I have and yes the 1 terminal needs to go to battery voltage key on. Now if you actually put a heavy diode inline on that you can run it from any 12 source key on in run mode(if it powers up in acc mode your alt will drain battery and can damage the regualtor.
As for runningthe 2 wire all over the car simply crimp and solder a 1/4 in ring terminal to it an loop it over the the battery terminal , nuch cleaner that way and less likely to have a 12 volts constant wire running all over the engine compartment, if you leave it in place put a 16 ga fuse link in it (crimp and solder andshrink tube the connection in any wiring goingto charging systems, electronics and computers.
I see guys spend thousands and never do a connection correctly.
It like they believe those elcheapo crimp terminal from big lots are gonna conduct current after a few months/years of water,dirt,corrosion invading them.
I am working on the pics on how to properly repair wires and a good reference on when/where you canget away with certain types of connections and hop to put it up so as to give better reference to some of the less informed/experienced hot rodders.
After having to build/rebuild all of the car I ever have had to depend on my wiring skills are pretty good and my techniques are from experience ratherthan a guess or just goin through motion to do something...oh and you can buy a form of shrink tubing that when you shrink it it glues itsself to the repair and seals out moisture. thesecond best repair is a crimp and seal type connector but it still has only a mechanical crimp by hand. and unless your had is bionic your never gonna make the heat,pressure nad control of a machine crimp, which by nature are so tight that corrosion is rare to infiltrate but it still getssometype of seal if its exposed.
Good luck on your alt project.
OH and if you would use the diode the band denotes a block of the voltage. Just put the diode with bad up and the arrow will point up and thats the side that goes to the alt. kind of like this [ I<---] arrow denotes direction flow is stopped.
Lee

[TheMonkey]

...
So, terminal #1 NEEDS to be hooked up to a Key On source in order for the alternator to function properly?

did you get this to work yet? i don't think that i saw it mentioned, but not only do you need term 1 hooked up to ignition, you also need some kind of resistance. the idiot light usually acts as the required resistance, but if you want to skip it, just wire a resistor in series in this wire. maybe 56 ohms, about 2.5 watts, doesn't take much.

[MonzaRacer]

Actually I have never had any trouble wiring them up to direct 12 volt key on power.
We have used them for years to conver early model tractors over to 12 volt neg ground systems as the generators are just lousy to keep running.
When the 10/12 SI (series integrated) alternator was first installed yes the older technology internal regualtors needed some form of resistance but after a few years the regualtor builders simply built a current limiter into that circuit so as to not have come backs if the unit is installed on something other than stock applications.
Now if you want that light to tell you that the regualtor/alternator failed run 12 volts from the key on run circuit ot the light bulb, then to the #1 terminal. What this does is when the power is lost from inside the alternator(ie its broke) the light will be grounded because if the alt has no out put the electronics simply stays grounded and the light is on.
But the light/resistor is no longer needed if you use a quality reman/new alternator.
Good luck
Lee Abel
AFTERMARKET PERFORMANCE