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battery drain


Dolfinz

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Well, I finally have the car running but now it appears I have an electrical issue.  When the battery has a full charge the car starts just fine but the alternator gauge has a slight negative reading.  After running for a bit and shutting it off, the car tries to start but since it has been running on the battery there's not enough spark.  I have a brand new alternator that clearly isn't charging the battery when the car is running.  Any suggestions as to what the problem could be?

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It could be the voltage regulator. Also, make sure you charge the battery fully. Running the car with a battery that is too weak/low can damage the alternator. Do you know how to use a voltmeter? You may also need to use an ammeter. This type can be helpful if you learn how to use it. https://www.amazon.com/Current-Auto-Ranging-Digital-Ammeter-V-Alert/dp/B094R8CB4W Until you can take some measurements and diagnose, you're just throwing parts at the problem. While you may be able to solve it that way, it tends to be more expensive.

Also, following what @Zed Headsaid, go to Account Settings (Click on the dropdown at your username if you're using a computer to access this site.) and then go to Signature. Put your car information in the signature. That will help people know what car you are working on. There are wiring differences between the years.

 

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I found an old thread.  Pretty much original owner.  So, external regulator, old alternator.  The VR's go bad eventually, but usually go high voltage.  Might just be a bad alternator.  Could even be a bad connection on the back of the alternator.  Pull them off and clean them up and see if things are better.  You'll need a meter like SteveJ says.

This is a sign that there's no alternator current - 

1 hour ago, Dolfinz said:

alternator gauge has a slight negative reading. 

 

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It's a 1974 260z Nov 73 production I have now owned for 44 years. As I stated the alternator is new.  Prior to rebuilding the motor it had no electrical issues.  But, it sat outside for a year and it dealt with monsoons and heat during the rebuild process during that time.  I know how to use a voltmeter and ammeter as I am an Electronic Engineer.  I'm just looking for somewhere to start.  Ammeter from alternator terminal to RW wire to confirm current is a start but what could be bleeding the current from there?  Possibly the shunt?  Isn't that the feed for the alternator gauge?  Why cant I just take the output from the shunt directly to the battery and bypass any potential bleeds?  I'm going to rewire the front harness myself and eliminate unnecessary wiring and get down to what's actually needed.  Is this a possibility?

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  1. Load test the battery to make sure it is good.
  2. Make sure the battery is fully charged.
  3. Download the FSM if you don't already have a copy. Focus on the EE section.
  4. Use an ammeter (not the gauge) to look for any drains on the battery. Hint: unplug the voltage regulator to see if that kills a drain.
  5. Test the charging system components, using the FSM as a guide.
  6. Make sure you are making notes on what & how you test with the readings/results so you can share with us along with details of what you have worked on/modified.

If you're not sure of how the charging system works, then I would advise against modifying the wiring. Especially with the 260Z, if you don't know what you're doing, you'll quickly wind up with a car that does not start.

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Those amp clamps are handy. I’ve got one with BlueTooth

I bought it when I went through swapping out 4 remanned alternators into my 4Runner. Yes the quality of remanufactured parts now is chit.


Sent from my iPhone using Tapatalk

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Can anyone tell me what the normal current draw for the battery should be?  I have studied the wiring diagram and the white/red wire from the alternator goes to the shunt and through the fusible link to the fuse block.  The white wire from the battery goes to the shunt and then also through the fusible link to the fuse block.  I will pull all the fuses and try starting it again and see if the battery charges but if it doesn't I can only assume there must be a partial short to ground in the harness somewhere.  Does this make sense?

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If you're talking about the draw with key out, and lights off, that could be anywhere from 0 to 25 ma, depending on car alarms or any other remote gear.

I paid $35 for my clamp-on meter from Amazon.  That particular unit isn't available, but they currently have a unit for $48.  Just be sure you get one that is good for DC current measurements; the cheaper ones are for AC only.

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On 8/18/2021 at 5:52 PM, Dolfinz said:

When the battery has a full charge the car starts just fine but the alternator gauge has a slight negative reading. 

The only draw on the battery would be the clock.  And that is so small that it won't drain a battery for months.

Still not really clear what problem you're trying to solve.  You showed that the alternator is discharging while the engine is running, which means the alternator is not working.  That will drain a battery pretty fast, with spark and fuel pump and various relays drawing power.

A super simple check for a key-off draw is to watch and listen for a spark when you connect the last battery cable.  I had a single relay active after a wiring change (alternator modification) and it created a significant spark, it was a clue that I had a problem (along with the battery dying overnight).  I think it was drawing 0.3 amps.  Once I fixed the draw even the clock didn't produce a significant spark even though it worked just fine.

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To verify the new alternator is not charging the battery,  measure the voltage across the battery with the ignition off, then measure the alternator output terminal with the car running, maybe 1000 rpm.   If they measure the same, the alternator is not providing a charge and the problem is likely a bad rebuilt / new alternator or as SteveJ has mentioned, the external regulator.  If the alternator is working, you should see somewhere near 14v on the second measurement.

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The engine is drawing on the battery not the alternator.  There is no draw when the key is off only when it is running.  This  is a second alternator and the engine has done the same thing with both.  The first one was only a couple years old and I had it tested and it was good but got a new one because the plastic cover on the back got lost.  I had the same problem with it before I replaced it so the alternator doesn't seem to be the problem.  Like I said previously, I'm going to pull all the fuses and see if that helps.  But now I'm thinking the engine won't run then because the electric fuel pump won't get power.  I'll try the measurements above but expect that if something is draining the alternator it's still going to look like a bad alternator.  I'll try it with white/red wire disconnected from alternator output.  As for the current draw, what would be the normal current draw to charge the battery while the engine is running and everything else is off?

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Sounds like your L wire is not providing power to the windings.  Check for voltage at the L wire with the key on.  A good alternator with no L power will not charge.

Actually with an external alternator, it's the F terminal.  No F power, No F'ing charging.  Check inside the plug with the key on.  sometimes the connection canget loose too, so if you find power make usre it's a solid connection to the F terminal.

Check your grounds also.  The alternator case should have a ground through the monuts but it also has a dedicated ground wire.  No ground no charge.

image.png

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Thanks for the advice.  I will check it.  I know it has a good ground as the black ground wire is connected.  It is possible that the F wire isn't a good con nection as the molded plug broke due to age and only the spade lugs are left.

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  • 5 weeks later...

Zed, It finally cooled down enough for me to work on the car.  So, as you suspected there's no +12 at the F terminal to the alternator, white/black wire.  I traced the wiring via the vehicle schematic and this wire goes through the voltage regulator and the electric fuel pump relays.  Any reason I can't just run a new wire from the ignition switch ON wire to the alternator?  It would save a lot of troubleshooting of the wiring in between if I can.  Let me know.

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Posted (edited)

I would check for power at the regulator plug from the main harness, and test for continuity from the regulator down to F.  The circuit could be broken before, inside, or after the regulator.

Looks like the switch powers the F wire and the L wire separately, in a parallel circuit.  I never really looked at the circuits in detail, for the internally regulated system they just use one L wire straight to the alternator.

I tried to post the FSM drawing but it failed.  It's on page EE-13.

image.png

 

Edited by Zed Head
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  • 5 weeks later...

I know it's been a while but I had to wait on a new voltage regulator; which I received and installed, and I've been working on getting turn signals, headlights, horn etc. operational.  This required having all my steering column switches rebuilt.  These are all completed and I'm back to addressing the alternator issue.  I have verified continuity of the F wire from the regulator to the alternator( this is a white/blk wire). What I haven't been able to determine is the color of the wire at the regulator plug that is supposed to go hot when the ignition is in the on position.  The white wire is constant +12,  the black wire wire is ground and the yellow wire goes to the alternator N terminal.  Can you advise as to the color of the wire from the harness that is supposed to be the IG connection?  The blk/ylw goes hot with the ignition switch on but if that's it why doesn't the wht/blk F wire get voltage?

I'd appreciate some further assistance.

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VR wire details.jpg

So when the key is on, the B/W wire has 12VDC. The Y wire will have about 7 to 8 volts with the alternator turning (full alternator voltage divided by the square root of 3).

The B/Y wire is just to provide a ground to the hell-hole known as the Ignition Interlock Unit (Boo! Hiss!) Chances are that it has already been bypassed in your car. Note that in other parts of your wiring, B/Y is 12VDC when the key is in start and goes to the Interlock Relay (Again, Boo! Hiss!).

B is your ground. W is your battery voltage and goes to the alternator through the WB wire when the appropriate contacts are closed.

 

 

Edited by SteveJ
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This is great info but I have a few questions.  You mentioned that the WB wire goes hot when the appropriate contacts are closed.  A prior post said the the WB wire should be hot when the ignition switch is in the ON position.  Does this wire not go hot until the engine is running and if so what activates the relay that closes the contact to make this happen?  My problem is that when the engine is running it uses the battery and the alternator doesn't charge the battery.  I assume that this relay must activate to excite the windings in the alternator so it charges?

Regarding the Ignition interlock unit you don't seem to like.  It can't have been bypassed as I would have had to have done it and I don't even know where it is located.  Is this something you would recommend that I do?  If so, please advise on how to do it and why you think it's a good idea.

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