Ok here is the deal, how do I tell if I have a oe wire alternator? Mine has a ground stud, a poitive stud and two spade connectors?

Now for the real problem. I have exhausted my wiring/electrical knowledge. I have the ground hooked up and the positive wire going to the battery. The positive battery cable goes to the starter. But when the truck is off I get 12.74 on the meter. When I turn it on it drops to 12.40 or so and even lower when the headlights go on. What am I missing? I have it wired in to a painless harness if that matters. Do I need the ampmeter hooked up? If so why does mie keep smoking the ground? Thanks

nope not a one wire sounds like you got the usual 3 wire,

ok i am missing something here or you forgot to state weather the truck is running or not cause when yaturn the truck on or the lights on the volts USUALY drop:flipoff2:

and what do you mean by smoking the ground?

this may or may not help you but heres what I used..http://www.derbypro.com/tut4.html

Before the early 70's, GM used the 10-DN series, externally regulated alternators. The terminals would be labled BAT (battery), GND (auxillary ground), R (field relay control for the indicator lamp), and F (voltage regulator).

The newer alternators are the CS series, and are 3 wire. They do not have a seperate ground terminal, so I don't think this is what you have.

I think you have an SI series alternator, because it has a ground terminal. On a running engine, the ground is not the negative battery terminal, it is the case of the alternator. Here's how to wire it:

The BAT terminal is the alternator output, and goes to the positive terminal of the battery.

The GRD terminal is an auxillary ground which should go to the negative battery terminal. Your main ground ground cable from the battery negative terminal (the big cable) should go to the block.

12 volts goes from the positive battery terminal, through the ignition switch, to the charging light, then to the number 1 terminal. It is used as the exciter (creates the magnetic field within the alternator).

The number 2 terminal is connected to the positive battery terminal, and is the feedback wire, used for voltage regulation.

BOTH THE NUMBER 1 AND 2 TERMINALS MUST BE CONNECTED, OR THE ALTERNATOR WILL NOT CHARGE.

Hope this helps.

Ok to clear a few things up. The truck off and the meter checking shows 12.70 or so. ie full charge on the battery off the battery charger. Now when I start it it drops to 12.50 or so and even farther when I turn the headlights on. Which indicates to me that the alternator is not recharging the battery. As for smoking what I meant is with the ampmeter wired up in series and I re connect the neg attery cable the ground starts to smoke. I sure hope I can get this worked out, so I can drive myself to work this week.

alternator or connection is fawked, you can get 100+amp gm 1 wires on e bay for under $75

ummm something is definatly not right check the wireing or by pass it like Stephen gave derections to

Sounds to me that you don't have a ground from the engine to the battery. It is using that small gage wire instead of a beefy cable, thus burning the wire.

Stephan has the right instructions for hookup. He is also probably right about the alternator being an SI. It Is probably a 10SI, which GM made millions and millions of. They came on just about every GM made between 72 and 83. You can tell by looking at the back of the alternator. You will see the rectifier behind the alternator housing. If there is three long slots in the housing for cooling holes to the rectifier, it is a 10 SI, if there are 6 rectangular holes it is a 78 AMP 12SI and if the fins on the rectifier are curved, then it is a 94AMP 12SI. There are 15SI, 17SI's but those are larger and I doubt you have one of those.

Anyways, it sounds like you have a short. It is not uncommon for this type of alternator to have a screwed up stator or rotor. It could even be the rectifier. To make a long story short, junk the alternator and go get a new one. To pay $75 bucks for one on ebay seems high, because all you have to do to make them one wire is to buy a regular 10SI and put in a Self Exciting regulator (one wire). 100 Amps is also easy to get out of ne of these units with a larger wire stator. You can buy a SE at any auto parts store the part number should be 7127-3 SE. You could probably buy one pretty cheap new $30-40.

If you actually want to get a good alternator, tell them you have a 86 VW Golf w/o Air. You will get a Bosch alternator that is better then any Domestic ever made.

Originally posted by Yo Mammy Boy
If you actually want to get a good alternator, tell them you have a 86 VW Golf w/o Air. You will get a Bosch alternator that is better then any Domestic ever made.

Woohoo..a whopping 65 amps! $120 for the alt with a $55 core? no thanks.

Bosch alternators are Delta connected, domestic alternators are "Y" connected. I don't think I can explane it right, it is somthing like this:

A "Y" connection is where the 3 phases of the stator are tied together at one point. A Delta conection is where 2 ends of 2 phases are tied together, so that if the windings are drawn in a schematic, the three phases form the sides of a triangle. Delta configuration is much more efficent and a 50-60 amp alternator in Delta can put out a lot more amps that a simalarly rated "Y" configure alternator.

Or at least that is how I understand it. Any electronics gurus wish to expand on this?

you say you are running an amp meter? what's the capacity? whats the amperage of the alt? if the alt puts out more than the amp meter can handle then you will smoke it. thats wyh most manufacturers switched to voltage meters when output went over 30 amps. there are aftermarket 60a meters, but they are spendy, and they require heavy gauge wire. now if you are hooking a wire from the amp meter to ground.. then duh.. you just created a short...... no wonder it starts smoking.. your lucky you burn that up and not the entire truck.., get your self a book at the liberary and learn how to wire stuff up!

Originally posted by Eskimo


Woohoo..a whopping 65 amps! $120 for the alt with a $55 core? no thanks.

Get one out of a Mekur Scorpio (sp?) 105 amp bosch with adjustable voltage.

Originally posted by Junkyard Slug
Bosch alternators are Delta connected, domestic alternators are "Y" connected. I don't think I can explane it right, it is somthing like this:

A "Y" connection is where the 3 phases of the stator are tied together at one point. A Delta conection is where 2 ends of 2 phases are tied together, so that if the windings are drawn in a schematic, the three phases form the sides of a triangle. Delta configuration is much more efficent and a 50-60 amp alternator in Delta can put out a lot more amps that a simalarly rated "Y" configure alternator.

Or at least that is how I understand it. Any electronics gurus wish to expand on this?

In electricity, nothing is free. You can trade volts for amps, or amps for volts.

Consider a pair of batteries. Each has a fixed capacity (total amount of power) available. Power (in watts) is equal to volts times amps.

If you hook those two batteries in series, you get a 24 volt system. The total power available remains the same, so if you utilize it at 24 volts, less current is available (volts times amps equals power).

If you hook the batteries in paralell, the voltage will remain at 12, but now more current is available. Again, volts times amps equals power.

An alternator is a three phase generator (uses three windings).

If the windings are connected in a wye configuration, at any given point in their rotation, two of the windings are in series with each other. Like the batteries, their voltages are addative. What this means, is that a wye wound alternator favors voltage.

If the windings are connected in delta, at any point in rotation, two of the windings are in paralell. Again, like the batteries, the delta wound alternator will favor current.

The biggest impact is at low rpm. The wye wound alternator will maintain voltage better, while the delta wound alternator can put out more current.

Originally posted by Stephenw


In electricity, nothing is free. You can trade volts for amps, or amps for volts.

Consider a pair of batteries. Each has a fixed capacity (total amount of power) available. Power (in watts) is equal to volts times amps.

If you hook those two batteries in series, you get a 24 volt system. The total power available remains the same, so if you utilize it at 24 volts, less current is available (volts times amps equals power).

If you hook the batteries in paralell, the voltage will remain at 12, but now more current is available. Again, volts times amps equals power.

An alternator is a three phase generator (uses three windings).

If the windings are connected in a wye configuration, at any given point in their rotation, two of the windings are in series with each other. Like the batteries, their voltages are addative. What this means, is that a wye wound alternator favors voltage.

If the windings are connected in delta, at any point in rotation, two of the windings are in paralell. Again, like the batteries, the delta wound alternator will favor current.

The biggest impact is at low rpm. The wye wound alternator will maintain voltage better, while the delta wound alternator can put out more current.

Thank You for saving me some typing.


Originally posted by Eskimo


Woohoo..a whopping 65 amps! $120 for the alt with a $55 core? no thanks.

Unless you have a big winch or 2000W stereo in your rig, the 65Amp Bosch is MORE then enough to power most rigs. If you do have a higher requirment for AMPS then get a bigger Bosch Alternator. The high output alternators, like a 100Amp 10SI are usually not as reliable. People buy double wound stators, which generate far more amps, but do not upgrade the rectifier and/or the diodes. They also generate a crap load of heat. The Bosch alternators are bulletproof, the only thing that goes wrong with these, usually is the brushes. And unlike 99% of the alternators out there they can be changed without pulling the unit off the vehicle. The aftermarket regulators on these are also adjustable. Its worth the extra $$ if you ask me. Lets not be Penny wise - Pound foolish.

Ok, thanks for all the help. Now if I decide to keep the alternator I have what do i use for the idoit light? or can I wire in a resistor? any part numbers or applications that I can get at Napa? Thanks and I am leaningt towards keeping the alt I have since I just bought it. Thanks

Any idea on how to tell the output on the bosch alts. Ther are a few saabs and other imports at the pick and pull that have the bosch alts on them. What should I look for??


-Darius