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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 07-11-2013, 12:58 AM   #1
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alternator not charging

My car is fucking broken someone help

Recently I swapped in a new engine room harness to replace my chewed up one. The new harness is from a base model 95 s14, my car is a 95 SE. There is a small difference in the fusebox on these which requires you to splice the alternator connection together.

See PAGE 32 from the EL section of the FSM.

http://www.nicoclub.com/FSM/240sx/1995/EL.pdf

You can see the connection that looks like a ground from the SE model needs to be spliced with the E18 connector from the base model fuse box.

I used one of these connectors from lowes to crimp them together because the gages are too big to solder.

http://www.lowes.com/ProductDisplay?productId=3370328

Next, after getting it started the alternator wasn't charging the battery and it would slowly die. I had them test it at autozone but it passed. I went ahead and bought a new one anyways. I've installed the new alternator and charged the battery back up to normal. Now the car stays at a constant 12~Volts when it should be reading 13-14V. Its strange because the car is NOT dieing out when I leave it running for a while, but the alternator seems to not be doing anything because if you take off the battery ground it dies. I don't know how the battery could be staying relatively constant with some electronics running if the alternator isn't doing anything?

All of the connections are tight including the belt tensioner. I've checked the shock tower ground that runs to the alternator. I'm really at a loss for what the fuck is wrong with it and I've been staring at the FSM for way too long. The 75 AMP fuse is not blown and I've even tried jumping the connection without the fuse. The 7.5 AMP fuse is also fine.

I've got 0.3V on the multimeter when I run the check from the ground on battery terminal to alternator casing and 0.5v when I run the positive terminal on the battery to the positive terminal on the alternator. I feel like if its NOT reading out at 13-14v the first time I take it for a drive its going to die on me if I just leave it alone even if its not dieing after 20 mins idling in the garage. I also got no change in reading when I revved the engine up.

I can't think of anything else I wanted to mention about the issue. I just want my damn car to run correctly.
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Old 07-11-2013, 01:24 AM   #2
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Is your battery/alt light in the dash on? Do the volts on the charging system increase if you add revs to the engine? Do you have the alt case ground attached? I believe there is a 8-10gauge ground on the case in factory form.

What are you getting for voltage at the alternator stud?
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Old 07-11-2013, 10:09 AM   #3
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I had this exact problem last year while swapping an engine. I used 3 different alts and triple checked every connection, fuse, and ground. It stayed at 12 volts and slowly went down from there.

It turned out to be the volt/alt signal wire going into the gauge cluster. Somewhere down the line there was an open in the wire. I did some research into this and some people were saying that signal wire tells the regulator to ramp up the voltage to 13.5-14. Others say that's not the case. The FSM makes mention of the charge indicator circuit numerous times when diagnosing a suspected faulty alternator. I would look there.
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Old 07-11-2013, 10:42 AM   #4
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Yeah I did see that in one thread from a search. Do you know which wire/resistor it is inside the cluster? I have a JDM cluster I could swap in to try it out.
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Old 07-11-2013, 11:01 AM   #5
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It should be the white/red wire from the alt running directly to the back of the cluster. Check pages 84-85 of the EL section on the link you posted.

Does your charge light illuminate when you turn your key to the ON position? This could be a case of a burned out bulb.
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Old 07-11-2013, 03:25 PM   #6
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Okay so the whole bottom row of idiot lights or whatever are NOT lighting up on either of my clusters when you turn the key to ON. Also, the light for the clock is on when the headlamps are off but when switched on it goes off? Do I have a plug mixed up somewhere maybe? Some of the lights come on for the cluster.

I noticed that when I checked the resistance for the resistor in the charge wire on the usdm cluster the resistance dropped to 10 ohms with the bulb in and goes back up to 100 without it where as the jdm cluster is always 100 ohm.

found a youtube vid with same problem

http://www.youtube.com/watch?v=80axdKIaSp4
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Old 07-11-2013, 03:52 PM   #7
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HOLY shit I fixed it. Motherfucking 7.5 meter gauge fuse was blown even though I had checked all the fuses a million times in this whole process. Getting 13.7 volts from the alternator now! Thanks for the heads up on that cluster circuit fucking up the alternator!
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Old 07-11-2013, 04:20 PM   #8
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Can you take pictures of the actual connection you made please?

edit: Nevermind, glad you fixed it.
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Old 07-11-2013, 07:38 PM   #9
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Quote:
Originally Posted by s0apgun View Post
HOLY shit I fixed it. Motherfucking 7.5 meter gauge fuse was blown even though I had checked all the fuses a million times in this whole process. Getting 13.7 volts from the alternator now! Thanks for the heads up on that cluster circuit fucking up the alternator!
Thats the fuse for the voltage regulator wire into the alternator huh? I was gonna say, check to make sure you're seeing voltage going into the 2 pin plug into the alternator.

Sometimes when that fuse blows, it does the opposite and the alternator overcharges since the alternator has no clue how much voltage its pumping out.
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