Find out what each pin of the upgrade GM alt does and connect to corresponding wire in stock circuit.

In stock circuit:
White "B" wire (heavy gauge) to the 80amp fuse
This is the battery charging wire.

White "S" to the 40amp (always-on) fuse
This senses actual battery voltage and should be connected as close as possible to battery positive. However, the way it is wired as-built (merely spliced with the B wire downstream of the Fusible link) it will read exactly alternator output and not battery output it is supposed to sense. Anyway, it will only be a small fraction of a volt off; no big deal.

Red "IG" to the Engine fuse
This provides (excitation) field current. This should have steady 12V when ignition is on (coming from Engine fuse). If no 12V here, trace wiring back to Engine Fuse, to "E" battery positive wire from fuse block.

Yellow "L" to the Charge Warning Light
This should be +12V when alternator is working properly (B voltage 13.5V-14.5V). If B voltage goes beyond that range too much, "L" will go low, and provided ground to negative side of the Charge Light causing it to come on.

 

The GM 10si and 12si calls for the L wire to be used as the field excitation wire. That's part of what makes this confusing.

 

Mind posting a schematic of GM circuit so we can analyze and find equivalent pins?

Excitation (IG) wire in stock has steady 12V when IGN is on.
Is L pin ON GM ALT connected to steady 12-V (from batt through Ignition switch) as well? If so, then yes, connect stock IG wire to Alt "L" pin.

How does GM circuit turn on "Charge Fault" light, by applying 12V to positive side? Or by applying low volt to its negative side? Toyota stock does latter through "L" output that goes low.

 

Wiring diagram for the typical 12SI:

http://www.rowand.net/Shop/Tech/imag...o1985Buick.jpg

Good question about the light. I think both the GM and Toyota systems work by causing the alternator side of the light to go low. Then the 12V from the ignition switch circuit sends current through it toward the alternator.

 

GM Wiring:


This is how I would wire it:


Single path for excitation current through Charge light bulb alone is not reliable; You know what happens to bulbs?

Resistor provides primary path for excitation current from engine fuse, and serves as "pull-up" resistor so negative side of charge light stays close to 12V (unless pin 1 goes low for actual charge fault condition). Without a pull-up resistor, excitation current may get high enough to turn on charge light and you'd get a false alarm. this is the reason for this:
Use same resistor value as GM's, and higher wattage if not same.

I would also move "B" wire from stock location in middle of fuse network to direct to battery positive [U]post[/U] (edit) with FL as close as possible to post. This will address "worst-case scenarios" I describe on my thread.

To maintain stock circuit protection scheme:

• Excitation current (through resistor) will be taken from stock IG wire coming from the engine fuse.
• Junction of IG resistor and Pin 1 will be on upstream side (away from wire going to dash) of charge fuse.

Also mirrored on my thread for easy reference later.

 

Let me see if I understand completely:

- Take the IG wire (12V always when key is on) from the stock alt harness, put a ~50 ohm resistor in series, and then connect it and the L wire in parallel to the field pin of the GM alt.
- Connect the stock B wire straight to the + battery. Actually, why not leave it where it is? If an additional, fused, heavy gauge wire is also connected from the atl post to the + batt, it shouldn't really matter. They could both connect to the alt post.

 

Exactly, but I missed a couple of things:
1) Drawing should show B wire with FL directly ON BATT POSITIVE POST
2) Use new B wire rated for new alternator capacity
3) Add appropriate Fusible Link (FL) to B a close as possible where it connects to battery post. This will protect "B" wire.Philbet has write-up on FL.

IF winch is used, it should connect directly to battery, before the fuse, just like starter positive (both draw extremely high currents).

For worst-case scenario explained in my post here.

 

OK. Now that I think it through again that makes perfect sense. Thanks for the help.

 

Updated drawing above for clarity and to reflect actual wiring. "B" Wire is directly on batt positive, stock 80 -amp fusible link (FL), stays between batt positive and fuse block to protect stock circuits as usual. All accessory circuits should be wired to battery positive through their own fuses. Current to after-market circuits will never pass stock FL. If anything goes wrong with after-market circuits, FL will not blow, keeping power going to stock circuits.

 

Rustbucket and guys,
I just realized that Buick drawing shows charge light connected to terminal X, and resistor is connected to terminal Y (below)



Does anyone know if X & Y they are actually same electrical point, OR is X the "Ignition ON" and Y the momentary-on "Start" terminal?

 

Good question. If the resistor wire was connected to the momentary-on circuit, it would still work since it would give the alternator field the initial excitation.

 

my 120 amp jaguar alternator was plug and play cost only $80 total $60 for the alt shipped and $20 including the tip to the machinist to get the toyota pulley machined to fit then i ran a 2ga wire to my battery with a lot of big grounds
http://www.ebay.com/itm/ALTERNATOR-Jaguar-XJ6-XJS-1993-93-1994-94-1995-95-96-678814-/310835563841?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1995%7CMake%3AJaguar%7CModel%3AXJ6&hash=item485f3e4d41&vxp=mtr

 

Thanks for sharing. Were the "IG", "S" and "L" wire plug and play, too? Or did you have to improvise as if using the Buick Alt above?

 

only wiring i changed was my charge wire to a 2ga

 

Well I got it all together tonight. The wiring as we decided on it works fine. Of course I haven't blown the charge light to check but the redundant voltage supply from the IG wire is included and isn't hurting anything.

Voltage at normal idle is a bit higher. Battery voltage with all accessories running and engine at idle is also higher, though not drastic. The new alt is a teeny bit noisy at slow rpms, kind of a slightly metallic noise. Maybe the brushes are wearing in?

The Trail Gear bracket works fine. It did require a couple washers as shims to get the new alt to line up perfectly.

Overall I'm happy with it. If I get bored with it I may take the Jaguar 120A alt route and sell my GM alt and wiring harness as a turnkey solution.

 

Cool! So how high is higher? Typical "B"voltage should range between 13.5 & 14.5V

 

I was getting about 14.5 before, now it's 14.7. I think the real test will be voltage with all accessories on and engine at about 2000 rpm. Unfortunately I forgot to test that with the old alternator :/

 

Hey Black_1985_SR5, do you have any pics of your Jag alt setup?

 

I've never heard of a case of the alt warning light bulb blowing out, in neither stock condition, nor from this type of a conversion.


never seen or heard of a false alt warning light condition from this, and the warning light bulb is supposed to go on, when the ignition is on, because the motor isn't running :-) so everything is behaving just like it did with the factory Toyota alt... although I suppose that an alternator failure will be the ultimate test :-0


congrats on getting it running, rustbucket!

 

dead wrong! from your link: "IF Battery Goes Out or is Disconnected, Alternator will provide necessary power to stock circuit and accessory circuits. Stock circuit protection stays unaffected."


here's a quick explanation of why that is a very bad idea:


"The moment he disconnects either lead from your battery, it's entirely possible he caused thousands of dollars in damage. Here's why...

Your battery does more than just yield electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car's stereo.

Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. If disconnecting the battery interferes with the voltage regulator's control voltage input, it's even possible for the alternator to put out hundreds of volts, frying everything.

Even the initial premise was wrong. If you disconnect the battery and the car conks out, you don't know if it conked out due to insufficient alternator current, or whether the resulting transients caused your ECU (the car's computer, which controls fuel mixture, timing, and much more) to spit out bad data, shutting down the car.

Nobody should EVER run your engine without a battery."
http://www.troubleshooters.com/dont_...ct_battery.htm