Can not get my alternator to charge

[86b240]

Howdy y'all I hope you guys can help me with my 4.0 swap issue I recently put a 4.0 in my 86 b2 used a 92 4.0 and a harness and computer outta a 91 explorer and for the life of me I can't get it to charge the battery I got power going through the larger yellow with white tracer wire to the alternator. I have the motor grounded to the frame and the frame grounded to the battery I started there figured that would be it I am now wondering if not having the green with red tracer wire hooked up which is the charge indicator light could be causing it. But I don't know how to proceed on that one new fuse in the power distribution box (I did check for power there but this was before I had power going to the alternator) It's also a brand new not reman alternator I don't have another to try and I don't want to buy another one unless I absolutely have to. Any ideas? Thanks for the read.

 

[RonD]

Welcome to TRS

Yes, you NEED that green/red wire for sure, it provides the startup voltage the alternator needs to start making its own voltage
It basically the ON/OFF switch so alternator doesn't drain the battery when key is off

So green/red wire needs to be a key ON 12volt, NOT full time 12v like the other alternator wires


An alternator is similar to an electric motor, just used in reverse
If you just left it ON with engine off, it would try to turn the fan belt, it can't come close, lol, but it would drain the battery trying
So alternator is powered OFF by 0 volt on green/red wire, key off

The battery light circuit is just a nice added on, if you give a light bulb 12volts that 12volts travels THRU the bulb and out the other side/wire

The other wire is the green/red wire, and when alternator is not spinning its at 0 volts, so it "acts" like a ground, and a bulb with 12v and "ground" lights up
When alternator starts to make its own voltage, that green/red wire is now 12v not a "ground"(actually its 14+volts)
If a light bulb has 12v on one wire and 12v on its other wire.....................then no light, its off
So when alternator is working the Battery light will go off, when its not working then battery light is on, if key is on

You can use any Key ON 12volt source for the green/red wire, but a Battery Light circuit is nice to have, because you won't know if alternator quits working until head lights start dimming or you get a "click, click, click", No Start

 

[86b240]

Thank you for the help so just so I understand greenlred to a switched 12 volt source should get me going. Do I have to have the light bulb for it to work ? Or can I add that in a later time like this winter ?

 

[franklin2]

You don't need the light. If later on you do get a light, it must have a plastic socket with two wires. The light is wired in series from the key to the alternator, and is not grounded.

 

[RonD]

+1 ^^^

2G/3G Alternator requires 3 wires connected to vehicle to work correctly

B+ wire, its on the back of the alternator on a stud/nut terminal, its a larger wire(or 2 wires) as it can need to pass up to 100amps at times, rating of alternator
B+ wire is connected to battery positive via a Mega Fuse or fusible link, always has 12volts

Yellow wire on voltage regulator inside 2G/3G alternators, on 3 wire connector
This is the monitor circuit for voltage regulator, uses a 15amp fuse or fusible link connected to battery positive, always has 12volts

Green/red wire, on/off switch for alternator, also on the 3 wire connector, has key on 12v, 0volt key off, also the battery light circuit

White wire on 3 wire connector, short jumper wire connected to single plugin on back of alternator, no voltage test for this one, just inspect it for frayed wires and make sure its plugged in

And thats all there is to the charging system as far as the vehicle wiring
If all 3 wire's voltage tests as OK and after start up battery still reads 12volts then alternator is bad, period