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Mystery Battery Drain in 1976 280Z


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My friend's 1976 280Z has suddently developed a parasitic battery drain. His charge light on the dash stays on indefinitely. He's put a lighted probe between the negative battery post and the negative battery cable and the light stays lit, no matter what fuse he pulls (short, right?). He's also pulled every fuse, one at a time, and the charge light stays on.

 

He hasn't touched the fusable links yet (I don't have them in my ZX so I'm not familiar) - could they be the cuplrit?

 

He's at wit's end trying to diagnose it. Radio is removed but still same symptoms.

 

I mentioned a "kill switch" in the cab, but that's a short term solution...would like to solve this once and for all.

 

Where would you guys start?

 

Thanks!

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Hmm, Electrical drains are always fun. I know the 280's pulse the injectors by pulsing the grounds. IT's pretty tough to say where the drain might be if he's already pulled all the fuses. The fusible links are higher amperage "fuses" as a term. I think all the vehicle power runs through them. but you should really look in the FSM/Haynes manuals for the wiring schematics about them. Is this something that just started one day, or has it been an ongoing problem? I'm sure you're testing the light between the neg term and neg cable with the Key in the off position right? Has the car had custom radio install? I'm wondering if there was a splice that was done incorrectly. With the cable connected & key off you could try using a meter to check various plugs to ground (frame) and see if you get voltage. The constant power wires should be very few in number. Another posibility is at the fuse box, you could use your meter there w/ fuses removed, one side of the fuses should be 0 volts, the other will show 0 to ground unless there's a leak. From there if you find power, you'd need to trace that line to fix a short.

 

Unfortunately electrical problems are a pain. on these old Z's too there's a large amount of corrosion in the plug connectors. so as you're tracing things, get some dilectric grease, and some terminal cleaner spray. Clean each connection you take apart, and put it togeter again with a little of the grease to help prevent trouble later on.

 

Sorry I'm not more help on this, Hopefully some of the other guys have more suggestions for you.

Phar

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Did you try disconnecting the alternator? I had one go bad and it constantly drained the battery.

 

 

 

Thanks Bartman.

 

I'm a n00b when it comes to eletrical gremnlins myself, and have been the victim of a dead alternator (on the freeway - really fun...).

 

My assumption is, however, that if the alternator is bad, wouldn't that just allow the battery to drain while the engine was running (since the alternator's job is to charge it while the engine is running)? Or, are you saying that the alternator is creating a contact beteween the battery and the body ground where it's not supposed to (because it's gone bad)?

 

easy thing to check....just want to understand the logic.

 

Thanks!

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I had my alternator fail at the Import Nationals at Carlisle last year. It created a short circuit so bad it vaporized my fusible link (like its supposed to do). When I took the alternator off I could hear something rattling around in it. It turned out that the diodes had broken off and fallen down inside the alternator housing creating a massive high amp short. Alternator would definatly be the easiest thing to check at this point. Instead of replacing the fusible link I installed an 80 amp fusebox. A little safer and cleaner than having a wire catch fire under the hood IMO.

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Thanks guys - this looks solid: http://www.datsunstore.com/product_info.php/products_id/1

 

 

 

NewZed - I assume you'd disconnect the battery ground before removing the "hot" regulator wire, correct?

 

Thanks guys - great information.

 

Phil

Yes, it's always a good idea to disconnect the battery ground when working on your electrical connections. And, I second the suggestion of ZMan's alternator upgrade. Good stuff.

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Thanks everyone - it WAS the alternator after all :)

 

UNFORTUNATELY, he already told the mechanic to replace it with a stock alt :/ I really lobbied hard for the higher amp one but it was too late! Shucks. I need to convince him to replace his fusible links, as I'm sure those are ready to catch fire sooner than later!

 

Thanks again for your help this week on this!

 

Phil

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