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Current draw traced to fusible link


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My 1976 Z has developed a parasitic current draw which drains the battery in a couple of days. I have traced it to the front right fusible link. That's the foreward one next to the fender, and it is brown.

My eyes aren't good enough to read the wiring diagrams, so hoping someone can give me a hint on what this link protects.

It started around the time I replaced the alternator with a new one from Autozone. I still have the external voltage regulator.

Any helpful advice is greatly appreciated.

Joe

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43 minutes ago, Humbug said:

My 1976 Z has developed a parasitic current draw which drains the battery in a couple of days. I have traced it to the front right fusible link. That's the foreward one next to the fender, and it is brown.

My eyes aren't good enough to read the wiring diagrams, so hoping someone can give me a hint on what this link protects.

It started around the time I replaced the alternator with a new one from Autozone. I still have the external voltage regulator.

Any helpful advice is greatly appreciated.

Joe

Have you measures the current draw?

Unplug the voltage regulator and see if you still have a current draw.

Edited by SteveJ
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You said the problem started shortly after you replaced the alternator. So as Captain Obvious, it is my duty to suggest you start your investigation there.

I suggest you disconnect your new alternator and see what happens.

Also, as a side note,,, For a 76, that front outboard link should be black, not brown. And it should be the largest link you have. That link powers a whooooooole bunch of stuff. Hopefully the issue is in the alternator and you can end the search with that.

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3 hours ago, Humbug said:

replaced the alternator with a new one from Autozone. I still have the external voltage regulator.

Why did you replace the alternator?  The VR has current path errors possible also.  If you were getting zero charge, probably the alternator.  Overcharge, probably the VR. 

And don't assume that Autozone gave you the correct product.  Could be they gave you an internally regulated alternator.

Here's a nice diagram.  Note that what people are calling Red now actually started as Brown.

 

Had it Copied, didn't Paste it.

 

Edited by Zed Head
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Thanks. I checked the diode in the alternator, and it passed, but I've not completely disconnected the alternator.

I rechecked the wire in the link, and it is blue.

I put a full charge on the red optima battery last night and fooled around with tests today. Then I left the battery disconnected. Later, when I checked, it had three volts,

I am going to get a new battery in the morning and start over.

Joe

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I replaced the alternator because it wasn't putting any charge at all to the battery. After I put the new one in, it didn't work, either. I later ravved the engine, and the alternator started working, putting about 14v to the battery.

Electricity is devious, in my experience.

 

Zed Head, I'm not seeing any diagram.

Joe

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did you completely disconnect the alt? that is both the large cable to the positive terminal as well as the two prong plug? as aready mentioned I wonder if you are mixing a internally regulated alt with a external VR, that would not be a good idea. 

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If you have a test light, use it between the negative post and the end of the battery cable before you connect it, with the positive cable connected.  The only draw you should have is the clock.  You could remove the fuse for the clock, whichever one it is, if you want to remove all potential draws.

You can also look for sparks, and/or measure amps drawn, depending on what tools you have.

16 minutes ago, Humbug said:

I later ravved the engine, and the alternator started working, putting about 14v to the battery.

This is what people have to do when their Field wire is not connected.  That comes through the VR.  Might be that your old alternator was fine and the VR is the problem.  Measure voltage at the bottom of the "T" in the plug at the back of the alternator with the key on.

image.png

Edited by Zed Head
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With the new battery, the alternator is making 16.4 volts, and there are some slightly melted wires in the harness at the voltage regulator, so I assume the VR is shot. I've ordered a new one, and will see where this takes me.

Joe

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2 hours ago, Humbug said:

With the new battery, the alternator is making 16.4 volts, and there are some slightly melted wires in the harness at the voltage regulator, so I assume the VR is shot. I've ordered a new one, and will see where this takes me.

Joe

Did you get a 40A alternator or did it have a higher rating? The 40A needs an external VR.

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6 minutes ago, Zed Head said:

76 had a 60A and an external VR.  

There's a procedure in the FSM for checking the VR.

D'oh! I was going from memory. I'm getting too old to do that.

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Replaced the VR and was getting 14.5 volts to the battery.
Noticed smoke coming from the VR. Didn't remove it to see the exact source.
I do get 12V to the stem of the T connection on the wire going to the alternator, with the key on.
I'm thinking I should remove the alternator and have it checked at Autozone, where I purchased it.Another option is to just buy the ZX alternator and install it. However, the problem may not be related to either the alternator or VR.
Does anyone have some sage advice for me?
Thanks,
Joe

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If you got 14.5 volts then the alternator was working.  With an external regulator you can get up to 15 volts.

I'd check the wires to the VR for short circuits to ground.  Where did you get the VR?  What brand is it?

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4 hours ago, Humbug said:

Does anyone have some sage advice for me?

My (hopefully sage) advice would be to start with the small, simple, obvious.

Take a pic of the back of your alternator and post it here so we can confirm that you have the right alternator. Start there.

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Another thought- make sure that the actual charging wire, the thick one that connects to B+ is intact.  The fusible link is one of the four in the two blocks up by the battery.  Check that black link.  Might be that the alternator is charging but there's no way for the charge to get to the battery and it's taking an alternate path.  Not sure how that would work, just a random thought.

Also make sure that the main ground cable is firmly connected at the starter bolt.  And that the black wire is connected to E at the alternator.  Might be that the problem is actually a ground path problem.

Looks like Nissan has it labeled "A" not B+.  You can see E also.

image.png

 

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Today, I cleaned the connections to the starter, put the VR back in, and everything seems to work ok. Getting 4.3 volts to the battery.

Maybe a bad connection there was the problem all along.

Thanks for Zed Head for the suggestion.

Tomorrow, I'll check for current draw. Hopefully, it no longer exists.

I'd have been really lost without the advice of you guys. Thanks for sharing your knowledge.

Joe

 

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