electrical issues on 77 280Z

[jcb]

I just acquired a 1977 280 and the battery will not stay charged. If the cable is removed it stays charged. It will not light a test lamp but a multimeter shows a 12v draw when placed between the ground cable and the battery post.

Also the tack is stuck at 3000 rpm with engine running or not. Thought someone might have had a similar problem and could offer a direction to go to find a cure for both problems.

I'm a returning member after a brief departure. Sold one 2 years ago but could not stay away from the allure of the early Z cars.

Thanks a lot for any help. John Butcher

[Dave WM]

15 minutes ago, jcb said:

I just acquired a 1977 280 and the battery will not stay charged. If the cable is removed it stays charged. It will not light a test lamp but a multimeter shows a 12v draw when placed between the ground cable and the battery post.

Also the tack is stuck at 3000 rpm with engine running or not. Thought someone might have had a similar problem and could offer a direction to go to find a cure for both problems.

I'm a returning member after a brief departure. Sold one 2 years ago but could not stay away from the allure of the early Z cars.

Thanks a lot for any help. John Butcher

most likely the clock. You need to switch to milliamp range (start with highest amp range so you don't smoke the meter) neg lead to neg post positive lead to neg bat cable (meter in series with neg lead). Read the current draw. IIRC the clock is something like 15ma so that is pretty much all you should see if all the lights are off. check stuff like glove box light going off when closed etc..

If you have a lot of current draw you could start pulling fuses one by one to narrow down the offending circuit.

[Zed Head]

1 hour ago, Dave WM said:

If you have a lot of current draw you could start pulling fuses one by one to narrow down the offending circuit.

Must not be much current.  It will kill the battery but the circuit has enough resistance that there's not enough current for a test lamp?  Seems odd.  

How fast does it die?  Has the alternator been converted to the internally regulated type?  There is a problem with some of the conversion procedures that are out there on the internet.

[jcb]

Zed, Thanks for the reply.I found the fact that it will not light a test light but still runs the battery down odd as well. I do get a reading of 12.6 v on a multi meter so I know it's going somewhere. I will try pulling fuses and see what I find. Thanks again. JCB 

[Dave WM]

could be a bad battery also. check the obvious 1st. the 12.6v you are reading does not tell anything, you need to check the current draw, if its low then the battery is most likely the problem.

[SteveJ]

The most likely culprit is in the charging system as Zed Head said. A bad voltage regulator will also kill the battery. Try unplugging the voltage regulator and see if the battery is dead the next day.

To Dave WM's point, will the battery start the car if you charge the battery? If it does, then continue diagnosing the electrical system.

Here's some tips on diagnosing: https://fiddlingwithzcars.wordpress.com/2012/12/16/some-electrical-basics-and-troubleshooting/

[SteveJ]

Also, if you aren't comfortable with using an old school ammeter, sometimes you can diagnose a current draw with a clamp ammeter like this: https://www.amazon.com/dp/B071SHLWTW

It will be a "Lightning Deal" on Amazon at 8:15PM Eastern Time on Friday.

[jcb]

Hi Guys, Again thanks to all who offered help on my problem. I got to check it again today and I find a .01 amp draw on the battery. If I have time tomorrow I plan first on checking the voltage regulator. Maybe that will do it.

Thanks again  JCB

[Dave WM]

Ok so the battery is discharging with a .01 amp draw overnite? is that right?

as far as the voltage regulator, just check the battery voltage with the car running, idle it should be around 13v with nothing on, with a load like head lights you will need to rev it to about 1.2k but it should maintain voltage around 13v if it does the charging system is fine.

So how old is the battery anyway? have you done an IR or load test on it?

[SteveJ]

Yeah, 0.01 A isn't going to drain the battery fast. 

[EuroDat]

Hi John,

 

Does the tacho go to 0 when you disconect the battery? If it does, it's your current draw. How it's stuck on 3000rpm is strange. Never seen one stuck before.

 

Does your clock still work? It will continually draw with a very small current. You can check it by pulling fuzes and see when it stops drawing current.

 

Btw Welcome back. Sadly, I know why you had to take time off, but its good to see you back again.

Ps. The tyre inflator looks great strapped in next to the space saver. Thanks again.

Edited October 1, 2017 by EuroDat

[jeremy93ls]

If the tachometer problem is unrelated and just needs repair like mine did, search for 'tachometer repair' on zdriver.com. I fixed mine with a $1 capacitor and a soldering iron.