RB20DET alternator wiring? custom swap but can't remember how it wires up.

[s13_240_rb20]

I am swapping this rb20 into a d21 and I have forgotten how it was wired in my 240. Can someone please spell it out for me? Or just tell me what "signal" each wire needs, like "12v switched" etc?? It cranks and runs and drives, but when I pull the POS+ battery post off it dies (and I have to jump it off cuz it doesn't charge) :*(

I am soooo close!! will post pics later.

I will list all of the wires below, please tell me whatever you know about any of them. I want to confirm the little I think I know.

Grey plug on alternator has:

Big solid white wiresmall white/red wire

There is also the big black and smaller black wires. Please confirm which is ground and which is POS+ and the POS+ ties into the main POS+ battery terminal, right??

Thanks,

--TJ

[s13_240_rb20]

I've been reading that the small white/red wire goes to the gauge cluster light so I assume that it is optional. But where should the bigger white wire be run to? And the POS+ and NEG- bolt on wires just connect to battery POS+ and ground, right??

[s13_240_rb20]

46 views and no replies yet, so I just want to ask a simpler question, I guess:

Can't I "hot-wire" my alternator to test it out????? (and rule out certain problems like "bad ground" "no power" "bad relay" "bad fuse" "bad whatever").

There are two small screws on the side of my alternator that I assume are there for a ground wire. I want to run a solid wire straight from a ground screw to the alternator and run a solid wire straight from the POS+ screw (bigger) and the white plug wire directly to the battery. Does anyone know of any harm in trying this?

p.s....from looking at the diagram for a 1994 q45 alternator, I am assuming that my solid white wire on the grey plug comes from the alternator FUSE in the fuse box and provides a POS+ signal for the alternator to "turn on"????

[s13_240_rb20]

wow....in a section of the site specifically devoted to the RB engines, no one has given a shred of advice on an RB engine component or even a "yay" or "nay" on my troubleshooting method I'm going to try....

sad

[datsunmotorsports]

I had a very similar problem wiring up my alternator. I installed a 25 into my old Datsun. The original Datsun setup had a externally regulated system.

The RB alternators are basically the same as the Q45 you found.

Ground the alternator body outThe big W/R wire goes to your battery. In the skyline it went to the fuse box where there was a bus post to power up the rest of the car and also tied directly into the bus post to the Positive battery terminal. Then you have a Field wire and a signal wire. This is where I am still fuzzy. You see one of these wires(which isnt colored correctly as in your Q45 schematic) should get a source voltage(+12V). This would be the one that goes through the 10A fuse in the diagram. The other is for is dummy light I believe. I tried to connect the Alternator without the dummy light hooked up. The Alternator would not charge! I simulated a dummy light with a resistor and the alternator started charging.

I know it isnt much help and I dont know which of the last two wires your looking for are colored, but it may be a stepping stone to finding what you need.

I have a charge light in my gauge now and I will be taking the time in the near future to wire it up.

[s13_240_rb20]

Thanks for the input....I'll go ahead and trace my trucks wiring for the dummy light tonight...who knows. That may be it?? Hopefully I won't have to source an alternator. It worked before I wrecked the car and pulled the engine.

--TJ


Modified by s13_240_rb20 at 12:06 AM 11/18/2009

[s13_240_rb20]

Anyone know if the RB alternator is, or if it can be, used as a "self-exciting" alternator??

I've also run across the info below that makes me want to hook up my white wire and white/red wire directly to the POS+ battery post.------------

3 wires are actually used plus chassis ground

There are 3 wires needed to run it and the case provides the path to chassis ground Even though there are 3 wires, it is very easy to wire up. Here's a desciption of the wires:

Battery positive (Bat+)

connect to starter +12V battery wire use 10 ga wire (thick) Screw on terminal on the back of the alternator

Voltage sensing line

connect to the Bat+ close to the firewall Senses and adjusts the +12V were it is needed use 14 ga wire (thinner) Pin 1 of the push in connector on the alternator

Ignition On input

When the ignition switch is turned on, power from the ignition switch turns on the alternator Pin 2 of the push in connector on the alternator use 18 ga wire

-----------------
Modified by s13_240_rb20 at 7:51 AM 11/18/2009

[s13_240_rb20]

OK....I am seriously losing my mind. There are two screw-on connections: I have 12v and I have the GROUND. Then there is the plug with a big white wire and a small white/red wire (charge light on dash?? dropping resistor???)

Well it seems that the previous post has some validity to it. I have the big white wire run to the battery also. With the white/red wire detached, it doesn't charge. Detached, the white/red measures .006v. When I attach the white/red to the battery, I instantly see the volt meter jump to 16v or so (CHARGING!!! I think??). But then the engine stalls in a few seconds.

It does that every time!!!!!

I have been searching all day for the correct wire in the engine bay (from the truck's dashboard charge light system), and couldn't ever seem to make it work with the wires I tried. every time it senses voltage given to the white/red wire, the engine stalls. Can anyone tell me what to do or if I can hotwire it some how and make it charge without stalling?? Or why it is stalling????

[s13_240_rb20]

Well, I guess in the morning I get to try it the way the picture and description above describe it. I can't even remember where I read that told me to wire it up how I did in the previous post (that stalls the engine when I connect the white/red to 12v).

WWCHD = What would Carl H do??? lmao anyone got his number?

--TJ

[s13_240_rb20]

Nevermind. Luckily, I figured it out by trial and error without frying my alternator.

On the RB alternator, the big white wire on the 2-wire plug is connected to my battery. And the small white/red wire is connected to the signal wire from the CHG lightbulb in the gauge cluster.

For future reference, there is a rectangular plug by the battery ON A NISSAN HARDBODY PICKUP and it has 4 wires to it. Since mine was an engine swap, my wiring stopped at the female plug. I ran the small white/red wire from the alternator plug to the yellow/black wire (the CHG signal wire) on the female side plug. That yellow/black wire measured about 6 volts and when connected to the white/red alternator wire, my voltmeter connected at the battery jumped up to 15v at idle.

As I have previously found out, connected the white/red wire to 12v caused the voltmeter (at the battery) to jump to 17v and the engine would stall in a few seconds unless I disconnected that white/red wire from 12v.

Lesson: 12v on the white/red causes overcharge?? 6v on the white/red causes 15v charging (which is good I'm pretty sure).

--TJ

[FerrariTruck]

thanks for the i

Nevermind. Luckily, I figured it out by trial and error without frying my alternator.

On the RB alternator, the big white wire on the 2-wire plug is connected to my battery. And the small white/red wire is connected to the signal wire from the CHG lightbulb in the gauge cluster.

For future reference, there is a rectangular plug by the battery ON A NISSAN HARDBODY PICKUP and it has 4 wires to it. Since mine was an engine swap, my wiring stopped at the female plug. I ran the small white/red wire from the alternator plug to the yellow/black wire (the CHG signal wire) on the female side plug. That yellow/black wire measured about 6 volts and when connected to the white/red alternator wire, my voltmeter connected at the battery jumped up to 15v at idle.

As I have previously found out, connected the white/red wire to 12v caused the voltmeter (at the battery) to jump to 17v and the engine would stall in a few seconds unless I disconnected that white/red wire from 12v.

Lesson: 12v on the white/red causes overcharge?? 6v on the white/red causes 15v charging (which is good I'm pretty sure).

--TJ

thanks for the info, just read it and looks like its giving me a heads up as i am now having charging promblems.