[DeTomaso] GM 12SI Alternator Connection ??? Resolved!

[Steve Liebenow]

OK, thanks to youse guys that responded with a good deal of information!
It is amazing what you can find on the web that is "close" but not complete!
Jon Haas had the most complete drawing, but his text was missing one terminal description.....
In short: on the GM 12SI alternator, Terminal #2 is for the sense or exciter lead connection.   The original wire on the old regulator was a yellow wire which ran to the hot side of the starter solenoid.    This can be reused to connect to Terminal #2.
What was missing most often was the description of what went to Terminal #1!    Turns out the most likely found description said use this lead to connect to your idiot lamp in the dash, if there is one.   You don't need one however, if you don't have a dash light!    I eventually confirmed that this is the case for the Pantera also.
Here's my story.......    So I connected it all up as above, found my cut off blue/black stripe wire that previously went to the regulator  (the PM that worked on this cut the danged regulator harness off in two spots.....duh!  And left the remainders in the bundles.....which led to more confusion until I discerned what had happened!   The yellow wire was cut off, and still connected to the hot lead...... such wonders never cease!    Disconnected it and tied it back.
I ran a new yellow wire or more accurately reused the wiring for the old Ford G3 alternator and spliced the new GM connector on to its two wired.   Fired up the car.....had a small hose leak....missed a clamp on final tighten...... but running well, charging, doing all the things it should do......except.....turn off!  Yup, run-on problem!  GM alts apparently are more susceptible to this, as the Ford G3, connected exactly the same, did NOT have a run-on issue.  Must be something in the internal regulator circuits that differs......
After going around and around, I finally got the thing to turn off, if I completely removed the Terminal #1 connection from the alternator. Hmmmmm.    Hitting the brakes, turning on fans (with the ign switch off) didn't kill the (supposed to be) residual current amount in the alternator.....!  Hmmmmmm.
Noticed that when I turned on the ignition switch to "RUN" that I didn't get a dash indicator!    SOBill's drawings indicate that there may be a "shunt" resistor across this bulb....in case the bulb burnt out, the old style regulator would not activate and you'd have no battery charge!
Well, fumbled around under the dash, only to find that not only were the wires not connected to a bulb socket, as they were shorted together, there was NO bulb and NO bulb holder!!! What!????    Did I get a spare bulb holder in the box of spare parts when I got the car?????? Need to go dig?
SO, having these two wires shorted out, allowed the engine to run on , self energized, even with battery completely disconnected!    My alternator expert recommended that when running an internally regulated alternator, you should have ONLY a bulb on this circuit and no shunt resistor.  If something ever happened to get this wire shorted, it could hose up the internal regulator....expensive repairs!    Bulb would act like a fuse at some point and save the alternator.
Still need a diode, a bulb  (124 or 1895?) and a bulb holder.  But I'm not going to worry about it this week!  Way loads of other stuff to work out before heading to Phoenix!!!   I just pulled the #1 pin out of the connector at the alternator, put an empty shrouded male spade connector on it, and tied it back away from any action!
Now the car shuts off without having to use a random gear and the clutch!!!  Just no idiot light at start up!  So easy fix.    I do need to rev the engine just a tad above idle to trigger the alternator to start working..... I can live with that..... alternator needle is rock steady also!   Something that was NOT the case with the big Ford alternator!
So all is well at least this far.   Tach is still on/off/mostly off......different day for that!   MSD and TA may be hitting the dumpster real soon. Put a DuraSpark II back in the car and never worry about it again!
Will finish fitting the new hatch cover for the hump reduction diet!   That can then be screwed in place, and I can start with the DynaMat treatment on the firewall. Hope it helps for my wife's sake!!!
Thanks again to all that sent me stuff!!!!
Steve
-------------- next part --------------
   OK, thanks to youse guys that responded with a good deal of
   information!
   It is amazing what you can find on the web that is "close" but not
   complete!
   Jon Haas had the most complete drawing, but his text was missing one
   terminal description.....
   In short: on the GM 12SI alternator, Terminal #2 is for the sense or
   exciter lead connection.   The original wire on the old regulator was a
   yellow wire which ran to the hot side of the starter solenoid.    This
   can be reused to connect to Terminal #2.
   What was missing most often was the description of what went to
   Terminal #1!    Turns out the most likely found description said use
   this lead to connect to your idiot lamp in the dash, if there is one.
   You don't need one however, if you don't have a dash light!    I
   eventually confirmed that this is the case for the Pantera also.
   Here's my story.......    So I connected it all up as above, found my
   cut off blue/black stripe wire that previously went to the regulator
   (the PM that worked on this cut the danged regulator harness off in two
   spots.....duh!  And left the remainders in the bundles.....which led to
   more confusion until I discerned what had happened!   The yellow wire
   was cut off, and still connected to the hot lead...... such wonders
   never cease!    Disconnected it and tied it back.
   I ran a new yellow wire or more accurately reused the wiring for the
   old Ford G3 alternator and spliced the new GM connector on to its two
   wired.   Fired up the car.....had a small hose leak....missed a clamp
   on final tighten...... but running well, charging, doing all the things
   it should do......except.....turn off!  Yup, run-on problem!  GM alts
   apparently are more susceptible to this, as the Ford G3, connected
   exactly the same, did NOT have a run-on issue.  Must be something in
   the internal regulator circuits that differs......
   After going around and around, I finally got the thing to turn off, if
   I completely removed the Terminal #1 connection from the alternator.
   Hmmmmm.    Hitting the brakes, turning on fans (with the ign switch
   off) didn't kill the (supposed to be) residual current amount in the
   alternator.....!  Hmmmmmm.
   Noticed that when I turned on the ignition switch to "RUN" that I
   didn't get a dash indicator!    SOBill's drawings indicate that there
   may be a "shunt" resistor across this bulb....in case the bulb burnt
   out, the old style regulator would not activate and you'd have no
   battery charge!
   Well, fumbled around under the dash, only to find that not only were
   the wires not connected to a bulb socket, as they were shorted
   together, there was NO bulb and NO bulb holder!!! What!????    Did I
   get a spare bulb holder in the box of spare parts when I got the
   car?????? Need to go dig?
   SO, having these two wires shorted out, allowed the engine to run on ,
   self energized, even with battery completely disconnected!    My
   alternator expert recommended that when running an internally regulated
   alternator, you should have ONLY a bulb on this circuit and no shunt
   resistor.  If something ever happened to get this wire shorted, it
   could hose up the internal regulator....expensive repairs!    Bulb
   would act like a fuse at some point and save the alternator.
   Still need a diode, a bulb  (124 or 1895?) and a bulb holder.  But I'm
   not going to worry about it this week!  Way loads of other stuff to
   work out before heading to Phoenix!!!   I just pulled the #1 pin out of
   the connector at the alternator, put an empty shrouded male spade
   connector on it, and tied it back away from any action!
   Now the car shuts off without having to use a random gear and the
   clutch!!!  Just no idiot light at start up!  So easy fix.    I do need
   to rev the engine just a tad above idle to trigger the alternator to
   start working..... I can live with that..... alternator needle is rock
   steady also!   Something that was NOT the case with the big Ford
   alternator!
   So all is well at least this far.   Tach is still on/off/mostly
   off......different day for that!   MSD and TA may be hitting the
   dumpster real soon. Put a DuraSpark II back in the car and never worry
   about it again!
   Will finish fitting the new hatch cover for the hump reduction diet!
   That can then be screwed in place, and I can start with the DynaMat
   treatment on the firewall. Hope it helps for my wife's sake!!!
   Thanks again to all that sent me stuff!!!!
   Steve