I've read all the 3G wiring conversion articles and I'm confused by every one of them!  Some say disconnect this wire, others say cut, splice into this, don't throw away that, etc., etc.  Therefore, I've decided to write a straightforward 3G wiring conversion article that, hopefully, anyone can understand!

Unlike most of the articles out there, instead of dealing with all the splicing and diceing, I decided to remove the entire factory alternator wiring harness and fabricate a new one.  It was really very simple.  Here's my stock factory harness.  The only thing to save here is the green w/red stripe wire.  Cut it right at the rear of the plug, then toss everything else in the trash!

Now, go the your local Pick-N-Pull wrecking yard and grab this connector/pigtail  with as much wire as you can.  This is the voltage regulator connector (also refered to as the D-plug) and the small grey connector attached to it is the stator connector.  The 2nd pic is a closeup of the inside of the D-plug.  This can be found on any 90's and up Ford with a 3G alternator.  Aerostar vans have them and are real easy to access.  In addition, find the starter relay on the fenderwell and remove the GRN 10 ga. wire with the big ring connector.  Now cut that wire just above the big rectangal rubber splice covering.  You'll be using that later.  You may have one on your Mustang that you can use.  I didn't.  The PO spliced a cheap orange 16 ga wire and cheap ring connector onto mine. 

Here's a pic of the back of the 3G altenator.  A = voltage regulator D-plug.  B = stator connector.  C = charge cable stud.

You'll need some wire to make your new harness with.  A length of 10 ga. for splicing to the YEL/WHT wire and a length of 18 ga. for the GRN/RED wire.  Now, attach the new GRN 10 ga. wire with the big ring connector to the post on your existing starter relay.  Plug your new D-plug and stator connector into the 3G alternator.  Measure the appropriate length of 14 ga. wire and splice that into the YEL/WHT wire at the D-plug pigtail and splice the other end to the GRN 10 ga. with the big ring connector (yes, you can splice 14 ga to 10 ga).

There, your voltage sensing wire is attached!

Next, measure the appropriate length of 18 ga. wire and splice that into the GRN/RED wire at the D-plug pigtail and splice the other end to the GRN/RED wire that you cut from your old factory harness (the one from the first pic).

There, the GEN light in you instrument cluster is attached!

Wrap the 2 wires in some quality 1/4" wire loom for protection.

FYI - to properly splice two wires together, they need to be soldered, taped and heat shrink wrapped.  Here is an excellent article on doing just that.............................

http://www.jalopyjournal.com/forum/showthread.php?t=318566&highlight=how+to+solder/

Next on the list is to fabricate your charging cable.  Before jumping into that you'll need to acquire a fuseholder and fuse to protect that high amp circuit.  Now, you can spend $25-$30 on an aftermarket fuseholder or you can be smart.  While you're at the junkyard grabbing the alternator pigtail, go find yourself a 90's Ford Contour.  There's millions of 'em there!  They have a transverse (sideways) motor.  On the back of the motor, between the intake and firewall, you'll find this fuseholder and fuse.  Shouldn't cost more that $2.

Onto charge cable fabrication.  Purchase a length of 4 ga battery cable ($2 per foot) and a couple of connectors ($3).  NAPA auto parts has everything you need.  First, mount your fuseholder as close to the starter relay as possible.  Then measure from the fuseholder to the charge stud on the back of the alternator (usually surrounded by a red plastic insulator).  Cut the length of 4 ga cable you'll need.  Strip a bit of insulation off the cable

Chuck a connector in the vise

 Get a roll of rosin core electronics solder and begin to clip off 1/4" pieces until the connector is filled about 2/3rds full.

Now, heat up the connector, using a small propane torch until the solder is liquified.  Immediately place the cable into the liquified solder and hold it for 15-20 seconds until the solder cools.

You can also place heat shrink tubing over the end to seal it.  Do the same procedure with the other end of the cable.  Now, attach the cable from the alternator charge stud to the fuseholder stud.  Measure from the second stud on the fuseholder to the stud on the starter relay and fabricate a second 4 ga cable.  Attach that cable and you've just completed your 3G wiring conversion!