Alt not charging

[ka-t]

i have a s13 redtop sr20det in a 1995 240sx , engine was pulled from my other s14 that had no charging issues . lower harness came out with the engine.

How i have the wiring setup
battery in trunk. power wire run to front of engine
using a large fuse block i have the battery wire and both white/red wires that go to the fuse box on one end and the large black/red wire out the other side.

I get 12v to the large black/red wire,so i know i have a good connection to there. Car starts fine but the alternator wont charge.

I have 1ohm through the black ground wire on the back of the alternator from post to chassi

Battery light is on and the brake light is on

I do get 12v to the wire on the connector to the alternator(yellow wire)

When vehicle is off and i check for voltage on alternator output post i have 9.09 volts and battery is at 12v. i know i have some kind or resistance in the wiring somewhere but when the car is running i have the same voltage at the post meaning that alternator is not putting anything out. so i pulled the alternator and put a ka alternator in there and tested again - still not charging

Any clues?

[wangan_cruiser]

contuinity test from the back 10mm nut of the alternator back to the fuse block that connects from the battery to the back. test it.

[ka-t]

so your saying test to see if i have voltage at the back of the alternator? serious ? because if i have perfect ground then my ground wire would be burning up!
Also i dont know if its a 10mm nut or 8mm bolt your talking about? no 10mm nut on a sr or ka alternator that i know of.

Also yes i will test tomorrow but if i have that happening then i surely should have blown fuse or 2 with voltage runing through my block

[wangan_cruiser]

the 10mm nut is the wire that goes to the 75amp from the fuse box then goes to the battery.

8mm is the ground and the 10mm is the wire that charges the battery. i had this problem last month that i had to swap 2 good alternators to fix the problem, then i accidentally hit the wire from the 10mm and it came off pretty easy.

[ka-t]

well i do get continunity because i have 9.09 volts there when the vehicle is off.So i do have a 3volt drop in the wire somewhere but its still connected. my problem is that im testing the output of the alternator at the power post and seeing nothing

[greenwood]

not sure if the same with your setup. On the RB20, there is a wire that goes from the alternator to a resistor on the dash. If not wired your alternator will not charge. When you turn your key on, you should see the alternator dummy light go on. Then when you fire it up it should turn off. If it is not doing either of these, then that is more than likely your problem.

[ka-t]

battery light is on so it sees its not charging.

I dont know what that wire does though. Does it send the cluster 12 volts from the alternator?

[GroundPerformance]

Verify the 75amp fuse.. and make sure the main power connection to the ALT is not shorting out.

[greenwood]

you need to have a wire running to that light on your dash. Or you can wire in a resist to make the alternator is hooked up to the dash light. It is a silly thing, but I'm pretty positive this will fix your issue. do searches to read more.

the little light is a form of resistor that lets the alternator know to start charging. without it no dice on charging anything.

[racecar11]

Can I get an update on what the problem was here? Im researching the same issue and need some more feed back.

[ka-t]

umm my update is that its working now and im and idiot - lol
i put the alternator wire from the alternator to the post in the fuse box . well that post went nowhere lol and the car i pulled the engine was wired differently . so all my fault

[vertsilvia93]

you need to have a wire running to that light on your dash. Or you can wire in a resist to make the alternator is hooked up to the dash light. It is a silly thing, but I'm pretty positive this will fix your issue. do searches to read more.

the little light is a form of resistor that lets the alternator know to start charging. without it no dice on charging anything.

how or where could I find out how to do this?

[greenwood]

how or where could I find out how to do this?

Sorry man, I posted that 8 years ago when I had a similar issue when I rb20 swapped my s13. You have to do some wire tracing or digging on the internet about the issue.

If you are going to tune/fix/tinker on these cars you have to use the wealth of knowledge already available. Guy mentions the charging dash light here as well. I found that info within a 10 second google search.

https://zilvia.net/f/showthread.php?t=634905

[greenwood]

Also if your intimidated by using a multimeter, dont be just watch youtubes on it and get one from harbor freight for 6 bucks they are cheap and work well.

[vertsilvia93]

Also if your intimidated by using a multimeter, dont be just watch youtubes on it and get one from harbor freight for 6 bucks they are cheap and work well.

trust me I have done hours and hours of research. I have a multimeter. The battery light on the dash is the exciter for the alternator. The light does not turn on when the key is on the on position. i am going to just run a wire directly from the alternator to the back of the gauge cluster. There might be a break in the wire.

[brndck]

trust me I have done hours and hours of research. I have a multimeter. The battery light on the dash is the exciter for the alternator. The light does not turn on when the key is on the on position. i am going to just run a wire directly from the alternator to the back of the gauge cluster. There might be a break in the wire.

so to take this conversation in a slightly different, but hopefully useful direction, when I ditched my stock cluster for a STACK cluster, my alternator would not charge upon starting up the vehicle. BUT, once I rev the engine to about 3-4k, it would kick on and begin charging. The stack cluster doesn't use any of the factory wiring, so the connectors for the factory cluster are just unplugged and left hanging.

long story short, the exciter from the cluster is NOT the only way to trigger the alternator. (I've had this stack cluster on 3 s13s now, same result on all 3 cars)

[vertsilvia93]

so to take this conversation in a slightly different, but hopefully useful direction, when I ditched my stock cluster for a STACK cluster, my alternator would not charge upon starting up the vehicle. BUT, once I rev the engine to about 3-4k, it would kick on and begin charging. The stack cluster doesn't use any of the factory wiring, so the connectors for the factory cluster are just unplugged and left hanging.

long story short, the exciter from the cluster is NOT the only way to trigger the alternator. (I've had this stack cluster on 3 s13s now, same result on all 3 cars)

HMMM this is new to me. So you've been running that stack cluster and the wire that runs from the alternator to the stock cluster is connected to nothing?

[brndck]

correct. my stack cluster does have a voltmeter built in, and you can monitor battery voltage. when you first fire up the car it will just sit static around 11.5-12v, and slowly you can watch it trickle down (takes a while, its not immediate), but if you free rev the engine (just once, above 3-4k, then let it sit back at idle), you can see the alternator kick on and start producing 13-14v.

I'm curious to see what anyone else with a STACK or AIM digital dash has experienced when deleting the factory cluster. Or even people who just ditch the cluster and use like Defi or greddy gauges.

[S14rebuild]

On my s14 i ditched stock cluster...i just ran the 12volt feed to the cluster to the alternator battery light wire on the harness and boom, alternator turns on and charges just fine...was super simple.

Alternator connector has key on 12v and a constant 12v feed from battery.. very simple

[vertsilvia93]

On my s14 i ditched stock cluster...i just ran the 12volt feed to the cluster to the alternator battery light wire on the harness and boom, alternator turns on and charges just fine...was super simple.

Alternator connector has key on 12v and a constant 12v feed from battery.. very simple

so just run a extra 12v source to the red and white wire on the dash cluster harness.

[S14rebuild]

Key on 12v wire.. yes.

But u should see why u dont have power there to begin with n fix that first

[vertsilvia93]

Key on 12v wire.. yes.

But u should see why u dont have power there to begin with n fix that first

im going to see why it isn't receiving a signal

[S14rebuild]

https://imgur.com/vo4O3v9



Here u go! Solve away lol

[vertsilvia93]

https://imgur.com/vo4O3v9



Here u go! Solve away lol

thanks so much!! im gonna look at it today.

[dbeiler]

so to take this conversation in a slightly different, but hopefully useful direction, when I ditched my stock cluster for a STACK cluster, my alternator would not charge upon starting up the vehicle. BUT, once I rev the engine to about 3-4k, it would kick on and begin charging. The stack cluster doesn't use any of the factory wiring, so the connectors for the factory cluster are just unplugged and left hanging.

long story short, the exciter from the cluster is NOT the only way to trigger the alternator. (I've had this stack cluster on 3 s13s now, same result on all 3 cars)

Nissan explained how this works in a TSB. Here's a quote from another alt thread I replied to:
Here is a paragraph from Nissan TSB NTB94-011 (page 4) to prove my point:

Charging System Operation When the ignition switch is in ON or START, current from the battery flows from the L terminal to the E terminal of the alternator, causing the CHARGE lamp to light up. Then when the engine is started, the voltage output increases as the alternator rpm increases. When the voltage output becomes greater than the battery voltage, current for recharging flows from the B terminal. Simultaneously, voltage at the L terminal disappears, causing the CHARGE lamp to go out. Note: It is possible for the alternator to charge, with the "L" circuit in operation by accelerating the engine so the RPMs are above 3,600. The current will raise high enough to complete the field current. The alternator will continue to charge until the engine is turned off. Alternator will not charge below 3,600 RPM because the field current has not been turned on by current induced by residual magnetism. Checking Terminal Voltage When diagnosing the charging circuit the same precautions and test methods as used for the starting circuit should be followed. Visually checking for wires and connections that are loose, corroded, chaffed, etc. can aid in the diagnosis process. The voltage drop method can also be used to isolate poor connections and unwanted resistance just as in the starting circuit.

[foreverdeath]

All you need to do to properly setup the alternator with a aftermarket cluster is wire a 12v key on engine on voltage source to the L terminal. This works with any alternator on my K swap i have the alt hooked up to the Haltech 12v engine relay. If there is no voltage sensed at this terminal the alternator wont charge.