3G Alternator Install: A How To

Discussion in 'Fox 5.0 Mustang Tech' started by Roland69, Jul 3, 2006.

  1. Apologize for the lack of knowledge here.

    Does the green/red wire going to the regulator act like a relay? the green wire doesn't pass along the current from the yellow wire over to the black white wire does it? I thought the yellow wire provided the power to the regulator? so if that provides power to the regulator, what does the green/red do exactly? why is it called an excite wire? does the white black wire feed power to the regulator or does it feed power to the stator windings?

    What i can't tell from the diagrams is the direction or flow of electricity. I'm assuming the black orange FEED power to the battery when the engine is running, but the black orange wire has power available from the battery when the engine is off..correct? Your alternator testing procedures have you check those black orange wires for 12 volts when the engine is off and when the ignition is off. And the fusible link in that circuit is to protect the battery from over charging from the alternator?

    The yellow sense wire, also has power from the battery when engine off and ignition is off, but when the engine is running, its detects voltage drop and tells the regulator to increase or decrease the voltage or amps going to the battery. the fuse in the yellow wire circuit is there to protect the alternator batt feed wires from blowing out the regulator?
  2. I finished the 3g alt upgrade today. thanks everyone for all your input
  3. I'm in desperate need of help. I ordered a 200 amp alternator to replace my current 200 amp alternator that was already on the car when I purchased it. The new alternator has the green wire removed from the plug and the yellow wire is run to the where the power wire goes . The white wire jumps off of the plug and into the plug on on the side of the alternator . Per rareelectric.com all I am supposed to do is connect the power wire to the terminal and because it is a one wire alternator. Is this correct? Also I will have to upgrade from the 4 gauge to the size you stated. My ground wire is the belt style hooked to the firewall is this the wire I need to upgrade as well?
  4. I am not familiar with the alternator you specified. You will need to contact the people that sold/manufactured the alternator.

    I also have no way of knowing how much current the ground wire you described is capable of handling.

    The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

    Any car that has a 3G or high output current alternator needs a minimum of a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

    A 200 amp alternator will need a cable larger than 4 gauge for both power and ground.

    Wire size current table:
    Dctaylor likes this.
  5. Thanks. I'm I will have those wires upgraded then do the install the way they specified. Which will have me leaving the current pig tail free and connecting the power wire to the back of the alternator. Which I don't see how that is going to send the charging level to the dash gauge.
    Thanks for your quick response.
  6. Tell me what you make of this...

    I've had a battery light that will come and go. Driving, sitting at idle, doesn't matter. It's been going on for a couple of years and I can't find out why.

    I have a PA performance 130amp alternator and an optima redtop which it located in the trunk with a master cutoff switch. I bought the optima in August of this year, so it's pretty new.

    First time I noticed it, I replaced the battery because it was old. It went away for a while and then came back. There was also another time when I went to go get a sticker and it was on for pretty much the 30 minute ride over and the 30 minute ride back home. I figured maybe the wiring from the alternator to the cutoff switch (charge wire) was messing with it, so I eliminated it and put it back to how it was.

    Well, tonight I went to go start the car and it stayed on the entire time. The battery voltage was around 11v. I cleaned the battery terminals and put the cables back on and the light went away...or so I thought. It was on and off and then back on again.

    When the light comes on, the needle is on the very lowest mark on the gauge. When the light goes off, it goes back up to about half. The only electrical draw I should have is the electric water pump and the 3 walbro 255's for the fuel pumps. Then of course the gauges/radio/lights/etc.

    Where should I begin looking??



    edit: i keep the battery on a tender

    So I went through the alternator troubleshooting checklist and have a question on engine not running, ignition on, battery charged #2. Mine measure 3.619/3.62. It's beyond the limits stated. What does that mean?

    Would shutting off your kill switch with the engine running damage the alternator?
  7. Shutting using the kill switch can damage the alternator. This is a right way and a wrong way for alternator kill switches.

    Your intermittent problem is probably in the alternator exciter circuit - warning light & green/red wire on the alternator. They likely cause is a bad connection (high resistance) panel connections. That would account for the higher voltage reading you got when testing that circuit

    See http://www.stangnet.com/tech/cluster87-93.pdf for information on the wiring differences, The clusters are interchangeable, but you have to do some trimming & move some wires.
    You will need the Adobe Acrobat viewer which is also a free download – http://get.adobe.com/reader/

    For a battery cut off switch, see http://www.moroso.com/catalog/categorydisplay.asp?catcode=42225
    is the switch http://www.moroso.com/catalog/images/74102_inst.pdf is the installation instructions.
    Use the super duty switch and the following tech note to wire it and you will be good to go.

    Use the Moroso plan for the alternator wiring and you risk a fire. The 10 gauge wire they recommend is even less adequate that the stock Mustang wiring.

    There is a solution, but it will require about 40' of 18 gauge green wire.

    Wire the battery to the two 1/2" posts as shown in the diagram.

    The alternator requires a different approach. On the small alternator plug there is a green wire. It is the sense lead that turns the regulator on when the ignition switch is in the run position. Cut the green wire and solder the 40' of green wire between the two pieces. Use some heat shrink to cover the splices. See http://fordfuelinjection.com/?p=7 for some excellent help on soldering & using heat shrink tubing.

    Run the green wire back to the Moroso switch and cut off the excess wire. Try to run the green wire inside the car and protect it from getting cut or chaffed. Crimp a 18 gauge ring terminal (red is 18 gauge color code for the crimp on terminals) on each wire. Bolt one ring terminal to each of the 3/16" studs. Do not add the jumper between the 1/2" stud and the 3/16" stud as shown it the Moroso diagram.

    How it works:
    The green wire is the ignition on sense feed to the regulator. It supplies a turn on signal to the regulator when the ignition switch is in the Run position. Turn the Moroso switch to off, and the sense voltage goes away, the voltage regulator shuts off and the alternator quits making power.

    The fuse & wiring in the following diagram are for a 3G alternator. The stock alternator uses a dark green fuse link wire that connects to 2 black/orange wires. Always leave them connected to the starter solenoid even if you have a 3G alternator.


    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring
    http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

    Ignition switch wiring

    Fuel, alternator, A/C and ignition wiring

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

    Vacuum diagram 89-93 Mustangs
    #127 jrichker, Oct 22, 2014
    Last edited: Oct 22, 2014
  8. Where should i start looking for problems in the battery light indicator circuit? I've unplugged the alternator D-plug and plugged it back in. Should I start with some dielectric grease? The cluster is from the factory, so the wiring is the same. I have my wiring exactly like the moroso diagram, minus the excite wire (trying to eliminate possibilities). It was suggested to run a 2ga wire from the alternator back to the battery in the trunk per the diagram below:


    The explanation was as follows: "You only have 1 wire from the battery, this shows 2 wires. The 1/0Ga is for starting, the 2Ga is for charging & sensing. You have no sensing at all. Do what I say & it's basically the same thing. 1/0 is larger than 0, so hope your load is not too big."

    I currently have the car wired as such:

    Attached Files:

  9. Your existing setup leaves a lot to be desired.
    The 2 gauge wire is expensive and adds complexity to the wiring, You have to route an extra wire that is large and not very easy to handle. Running two 16 or 18 gauge wires is much less expensive and easier to do.

    Wire size is important: too small a wire will overheat and catch fire if it is not protected with a fuse.
    Undersize the wire and oversize the fuse it or, no fuse, and the voltage drop across the length of the wire will seriously affect the available voltage to the electrical system. That will lower the needed voltage for the computer, ignition, fuel pump, lights, etc.

    Wire size current table:

    Use a DVM to measure the resistance between the green/red wire on the instrument panel connector and the green/red wire on the D plug on the alternator. You will need to disconnect both plugs to get access to the wiring connectors. You should see less than 1 Ohm resistance between the two ends of the wire.

    Inspect the instrument cluster for evidence of corrosion or damage. Minor corrosion can be removed with a Scotch-Brite green scrubber pad, just don't get too vigorous scrubbing the flex circuit.
    #129 jrichker, Oct 24, 2014
    Last edited: Oct 24, 2014
  10. I set my digital meter to Ohms and with both wires disconnected from their harnesses, it read 4.1 - 4.3. After leaving it for a few minutes, it settled at 4.1. What is this indicative of?

    I appreciate your help and your patience,

  11. One meter lead goes on the dash green/red wire connector and the other meter lead goes on the alternator D plug green/red wire connector
    You should see 1 ohm or less. if not, you have some dirty contacts or some defective wiring in the green/red wire between the dash and alternator.
  12. The contacts looked clean on both ends and none of the stock wiring was touched. I did have to solder the green/red back together after removing the wire that runs to the master switch in the rear. I wonder if I take a pin and test it after the soldering joint if it will read different. I will try that and report back.

    Thank you again!
  13. By touched I mean extended
  14. Without touching anything it now reads 1.3-1.4. I literally turned it on without touching anything from the prior reading
  15. there's a blue connector that has some green sludge in it. I will try cleaning the blue connector along with the connector at the dash and the alternator. Hopefully this will solve the problem. One thing I did notice when I was taking the wiring out of the loom, the green wire looks like it was stuck to the yellow wire, but no wiring was pushing through/touching eachother.
  16. You are getting closer to the required results. Keep working at it...
  17. testing both sides of the connector, each measure at .3-.4. so from the D-plug to side A of the blue connector and then from side B of the blue connector to the dash. It had to have been the blue connector, right?
  18. Since I can't see what is going on, I'll take your word for it.
  19. Well, that fixed the issue. Thanks for your help!
  20. Hey guys sorry if I'm asking a question that's been beaten to death already, but better safe than sorry. I guess my confusion comes from reading into the install too much and having several information sources. Question is, Has there been an update on how to tackle the wiring mod? I saw somewhere that the green/red wire on the regulator harness is then hooked up to the alternator's output post with the power wire.

    Another thing is, on the white/black wire, I know it goes to the stator plug, can I just cut it from the regulator harness, so it just goes straight form that harness to the stator? that means the old power wire and the white/black wire with it gets taped up.

    Again, sorry, I know some of my questions have been asked and answered a billion times.

    Here's what I have so far 1479335004667-291801793.jpg