3g Upgrade Plug Question

are you getting the alternator from the JY ? if so clip the plug and splice it into the harness. My last go around I purchased a wiring kit which had everything pre-measured and crimped that came with a plug that you also spliced into the harness. stock gauge is still functional.

http://www.stangnet.com/mustang-forums/threads/3g-alternator-install-a-how-to.646825/#post-6673702

Alternator wiring.





Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 Model cars.



Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.

In addition to the new 4 gauge power wire with an inline water tight 150 amp mega fuse, all you need to do is take the existing D shaped plug from your 2G and plug it into the same D shaped receptacle on the 3G. and tap into the stator wire in your existing 2G wire harness and attach it to the male stator connector on the 3G with either the correct stator connector or you can use a female connector. You do not need to cut any wires from the 2G power plug. Just tape it off and tuck it away.

did you hook up a DVM and check the volts at the back of the alt and also the battery at idle and at 2000 rpm? Did you add an additional 4g ground wire from the engine to the ground post behind the battery.

The wiring is very straight forward. 4g power wire from the power post on the alt to the battery side of the solenoid. Splice the stator wire from the stock power wire plug into the connector on the alternator. Make sure the power and stator wire are not touching ground. Make sure all the connections are tight and properly fastened- I solder and shrink wrap when possible. Finally just because AZ tested the alt once doesn't mean it is good.

Grabbin' Asphalt said:

replaced fuel filter, no change. no drop in fuel pressure either when it skips stalls 3000-3500rpm. Only when i turn my headlights on or use a/c. Does not skip when they're off. ....where should i look???

Click to expand...

check your ground strap from the firewall to the back of the block. That is for the gauges and the A/C. If you have alum heads relocate the ground strap to the block instead of the head.

Grabbin' Asphalt said:

Well I got these readings today.

Engine off:
battery + - = 12.65v
Alt stud= 12.65v

Engine idle:
Battery + - = 14.44
Alt stud = 14.44
Alt stud with headlights, electric fan, a/c high= 13.35

maybe i have a clogged fuel filter causing hesitation??

Click to expand...

Guess what?
If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

A 1 volt drop at full load is a pretty serious drop in a 14 volt system. 13.35/14.44 = 7.55% voltage loss.


If you did run the white/yellow wire to the starter solenoid, then you definitely have a problem. Check the power feed wiring and fuse holder on the alternator output and the starter solenoid connection for voltage drops. Then check the ground between the alternator case and the battery negative terminal for voltage drops. Here's how to find the problem using a voltmeter to check for voltage drops

Voltage drop testing of connections and grounds.

Use a Digital Volt Meter (DVM) to measure the voltage drop across a connection or wire. Adding length to the test leads may be required, and does not affect the accuracy of the test. Use 18-20 gauge wire for the test leads if you have to lengthen them.

Voltage drop testing must be done while the usual load is on the circuit. If it is a starter, it has to be tested while cranking the starter. If it is lights, A/C or fan, they must be turned on high while testing. Fail to do this and you will not get accurate results

1.) Most grounds use the negative battery post as their starting point. Keep this in mind when checking grounds.
2.) The voltage will be small if the ground is good: less voltage drop = better connection.
3.) Be sure that the power to the circuit is on, and the circuit is being used in its normal manner. For instance, if it is a light circuit, the lights on that circuit should be powered on.
4.) To measure grounds, place one DVM lead on the battery negative post and the other on the wire or connector that goes to ground.
5.) Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections (sensors are low voltage devices and small drops can have a large effect on the devices dependent on sensor accuracy)
0.0V Connections
A voltage drop lower that spec is always acceptable.
6.)
See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. . I recommend that you save the PDF doc for future reference.

jrichker said:

Guess what?
If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

A 1 volt drop at full load is a pretty serious drop in a 14 volt system. 13.35/14.44 = 7.55% voltage loss.


If you did run the white/yellow wire to the starter solenoid, then you definitely have a problem. Here's how to find it using a voltmeter to check for voltage drops.

Voltage drop testing of connections and grounds.

Use a Digital Volt Meter (DVM) to measure the voltage drop across a connection or wire. Adding length to the test leads may be required, and does not affect the accuracy of the test. Use 18-20 gauge wire for the test leads if you have to lengthen them.

Voltage drop testing must be done while the usual load is on the circuit. If it is a starter, it has to be tested while cranking the starter. If it is lights, A/C or fan, they must be turned on high while testing. Fail to do this and you will not get accurate results

1.) Most grounds use the negative battery post as their starting point. Keep this in mind when checking grounds.
2.) The voltage will be small if the ground is good: less voltage drop = better connection.
3.) Be sure that the power to the circuit is on, and the circuit is being used in its normal manner. For instance, if it is a light circuit, the lights on that circuit should be powered on.
4.) To measure grounds, place one DVM lead on the battery negative post and the other on the wire or connector that goes to ground.
5.) Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections (sensors are low voltage devices and small drops can have a large effect on the devices dependent on sensor accuracy)
0.0V Connections
A voltage drop lower that spec is always acceptable.
6.)
See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. . I recommend that you save the PDF doc for future reference.

Click to expand...

j, if he left the yellow wire hooked up on the solenoid and spliced into the stator wire in the original alternator power plug and then attached that to the stator connector on the 3G, wouldn't that work? Unless I missed it, did he say he disconnected/bypassed the yellow wire ?

mikestang63 said:

j, if he left the yellow wire hooked up on the solenoid and spliced into the stator wire in the original alternator power plug and then attached that to the stator connector on the 3G, wouldn't that work? Unless I missed it, did he say he disconnected/bypassed the yellow wire ?

Click to expand...

That sounds just like what I previously posted...