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Old 09-06-2016, 05:50 PM   #1
Stancyeze
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SR20DET Alternator Not Charging

I have a '96 240x with a S13 Sr20DET redtop motor set swapped in to it. I did the swap about a month ago. The car has a new WiringSpecialities harness in it and a RS Enthalpy ROMtune on the ECU. Ever since I've gotten the car running I've had a battery/charging issue.

I replaced the battery twice and just did the 115amp Nissan Quest alternator upgrade with CodyAce's kit. The battery hold 12.45 volts with the car off. Once started it drops to 12.04. Checked alternator relay and it's good. One thing that concerns me is there is no battery light coming on on the dashboard... So I'm assuming the dash is not getting a signal from the alternator, but I'm not sure if the OBD1 engine would do this to the OBD2 car.

Anyway, if anyone has any insight... please don't hesitate to help!
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Old 09-06-2016, 06:46 PM   #2
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Here's how your charging system works:
You have four wires running to your alternator.

The black wire is obviously the ground wire. The alternator will also be grounded through the engine block so technically you don't even need that wire.

The heavy white (or black/red depending on model) wire is used to send current produced by the alternator to the fusebox. The current passes through a 100amp (or 75amp depending on model) Maxifuse in the fusebox. Yes you read that correctly. A 100amp fuse. If your so-called alternator 'upgrade' was ever to actually produce maximum power, the Maxifuse would blow. Quest alternator 'upgrades' are unnecessary. 240s don't require this much power. This heavy wire is also irrelevant to alternator operation. The alternator will produce voltage without anything attached to that terminal. The wire and Maxifuse must be operational to recharge the battery though.

The small yellow wire is used to regulate the alternator output. It receives battery operating voltage through a 7.5 amp fuse in the engine bay fusebox. In laymans terms, it sends a battery voltage signal to the alternator so it can vary output and produce a nice, steady current regardless of speed or load.

The small white/red wire runs to the charge indicator bulb in the gauge cluster. This wire and it's operation is VERY important because it carries the power necessary to bring the alternator to life.

In a fully functional system, when you turn the key on, the fusebox in the left kick panel comes to life. A 7.5amp fuse in there sends 12v straight to the charge indicator bulb. The other side of the bulb is that small white/red wire running to the alternator. The alternator field circuit grounds that wire and, of course, the bulb lights up. Once the alternator is spinning fast enough, it'll produce your car's operating voltage. The voltage will now be equal on both sides (or 'legs') of the charge indicator bulb. Current cannot flow with equal voltage. The charge light will extinguish. You'll know the system is working correctly.

If your charge indicator light doesn't illuminate when you turn the key on, you've already narrowed down the problem. That 7.5amp fuse is blown, the charge indicator bulb is blown out, the gauge cluster is disconnected, the alternator field circuit is faulty and isn't grounding the bulb, or you have a broken wire in the charge indicator circuit.

OBD won't have anything to do with the charging circuit.
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Old 09-06-2016, 07:04 PM   #3
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Quote:
Originally Posted by dbeiler View Post
Here's how your charging system works:
You have four wires running to your alternator.

The black wire is obviously the ground wire. The alternator will also be grounded through the engine block so technically you don't even need that wire.

The heavy white (or black/red depending on model) wire is used to send current produced by the alternator to the fusebox. The current passes through a 100amp (or 75amp depending on model) Maxifuse in the fusebox. Yes you read that correctly. A 100amp fuse. If your so-called alternator 'upgrade' was ever to actually produce maximum power, the Maxifuse would blow. Quest alternator 'upgrades' are unnecessary. 240s don't require this much power. This heavy wire is also irrelevant to alternator operation. The alternator will produce voltage without anything attached to that terminal. The wire and Maxifuse must be operational to recharge the battery though.

The small yellow wire is used to regulate the alternator output. It receives battery operating voltage through a 7.5 amp fuse in the engine bay fusebox. In laymans terms, it sends a battery voltage signal to the alternator so it can vary output and produce a nice, steady current regardless of speed or load.

The small white/red wire runs to the charge indicator bulb in the gauge cluster. This wire and it's operation is VERY important because it carries the power necessary to bring the alternator to life.

In a fully functional system, when you turn the key on, the fusebox in the left kick panel comes to life. A 7.5amp fuse in there sends 12v straight to the charge indicator bulb. The other side of the bulb is that small white/red wire running to the alternator. The alternator field circuit grounds that wire and, of course, the bulb lights up. Once the alternator is spinning fast enough, it'll produce your car's operating voltage. The voltage will now be equal on both sides (or 'legs') of the charge indicator bulb. Current cannot flow with equal voltage. The charge light will extinguish. You'll know the system is working correctly.

If your charge indicator light doesn't illuminate when you turn the key on, you've already narrowed down the problem. That 7.5amp fuse is blown, the charge indicator bulb is blown out, the gauge cluster is disconnected, the alternator field circuit is faulty and isn't grounding the bulb, or you have a broken wire in the charge indicator circuit.

OBD won't have anything to do with the charging circuit.
Checked the 7.5 amp in the kick panel and the one in the engine bay fuse box. Both tested fine and are working. The dash bulb being out is unlikely, but a possibly. Gauge cluster is not disconnected, so the only thing it could be out of your options is a broken wire in the indicator circuit. But the car previously ran with a KA so I don't think that's it.
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Old 09-06-2016, 07:37 PM   #4
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The field circuit is inside the alternator. It could be a faulty alternator.

Are you proficient with a meter? You need to check for voltage at the small white/red wire on the alternator.

Also, you can disconnect the alt connector and do a continuity check through the field circuit to ground.
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Old 09-06-2016, 07:38 PM   #5
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Voltage check must be done with key on.
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Old 09-06-2016, 07:40 PM   #6
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One more option. When you disconnect the alt connector, jump the small white/red wire directly to ground. Charge indicator light should illuminate with key on.
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Old 09-06-2016, 07:44 PM   #7
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Quote:
Originally Posted by dbeiler View Post
Voltage check must be done with key on.
Right, well i don't think any of the wiring could be bad as its a brand new harness. It's an error on my end I'm thinking. Wiring Specialities send you a harness that is universal with any S14 so there are going to be connectors that don't get used. I'm thinking I didn't plug something in or something like that, but as far as I can see I have everything plugged in so I'm going to give W.S. a call in the morning and maybe try to figure it out that way.

Could be a bad alternator, it would just be odd since its a brand new OEM alternator. But you never know... haha.
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Old 09-06-2016, 07:57 PM   #8
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Right, well i don't think any of the wiring could be bad as its a brand new harness.
The W.S. harness has nothing to do with the charge indicator circuit. That circuit follows through the engine bay harness into the cabin through the body grommet on the driver side.

Pull out your multi meter and check for continuity between the engine fuse box plug and the back of the gauge cluster.
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Old 09-07-2016, 08:31 AM   #9
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Quote:
Originally Posted by Agamemnon View Post
The W.S. harness has nothing to do with the charge indicator circuit. That circuit follows through the engine bay harness into the cabin through the body grommet on the driver side.

Pull out your multi meter and check for continuity between the engine fuse box plug and the back of the gauge cluster.
I'm going to check the instrument cluster bulb first, and then go from there.
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Old 09-07-2016, 09:16 AM   #10
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Bulb tested good.
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Old 09-07-2016, 11:56 AM   #11
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Turns out my main power wire wasn't hooked up to the fuse box haha. I had it hooked up as a ground to the chassis as I assumed it was because it had an eyelet on the end. But now all is good!
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Old 11-18-2019, 03:27 PM   #12
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I'm having this same issue and I cant figure it out!!!!!
my battery light isn't turning on.
New alternator, every fuse is good, I've tried 3 alternators.
I'm so stumped!!!
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Old 11-19-2019, 02:45 PM   #13
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check continuity on the wires in the system...
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