Skidog214

A few months ago, I acquired a 1985 wide body cab. At the time, the dealer said he put a new battery in the car because the one that was in the vehicle was the wrong size. The car has been running fine. Yesterday, I go start the car and there is a “click” when I turned the key and the battery is dead. I look at the batter an it has handwritten “03-14” on the top. I don’t know if that means it is old (from March 2014) or something else. So, I get a jump, and drive to an auto parts store to replace the battery. When I go inside to see if they have the right battery, I leave the car running because I am afraid if I turn it off, it won’t re-start. The store has the correctly battery, so I go back outside to turn off the car, and the car has quit running! The key is still on, but the car is dead. I put in a new battery and the car starts, no problem.

So, my best guess is that the battery may have been fine, but that the alternator/generator was not charging the battery. I am guessing that the car ran on the battery until the battery was exhausted and just quit. I intend to drive the car to my mechanic to have him check it out, but would be grateful for your thoughts/input. What do you think is wrong?

As always, thank you to those who respond!

IXIXI

I have used this cheap tool for 30 years and carry one in every old car. Easiest way to spot a charging system problem IMO.

Skidog214

What is it?
Where does one get it?
What does it do?
How does one use it? [I am guessing you insert it into the cigarette lighter, but I went to public school so you never can tell!]

Thanks

Skidog214

Typed too quickly! So, it is some kind of volt meter! If I can find one, what do I want it to show when inserted into the lighter receptacle?

IXIXI

At a glance…
Resting voltage (engine off) should be 12.6 plus or minus
Battery low voltage of 12.2 or lower is a bad sign of battery health or discharge
Running car over 1800rpm or so with healthy/charged battery 13.5v plus or minus. RPM will change this momentarily
Running car showing 14.4 or higher to 14.8ish the battery is pulling a strong charge. This will slowly drop volts over time as you drive.
Running car over 16.5v the regulator has a sever problem.

This is a simplistic look at things but at a glance can show what the current state of the charging system is at.

theiceman

be careful with this one .... as its tricky..

Yes every classic 911 owner should be running a voltmeter ( for over voltage as well as under ) .. the one for the lighter will likely fall out though if it has the European socket. Wire one in.
the alternator light should have been on indicating the alternator is faulty and not putting out 12v. Sounds like it wasn't.
does that alternator light come on with just the ignition on ?
I have read that the instrument dash light acts as an exciter for the circuit and if the bulb is blown it wont charge the battery .. not sure how true that is though ...

Also could be as simple as the a battery post connection, mine come loose occasionally as its so awkward to get in there and tighten it , it will obviously stop the car from charging as well as starting.

so a few things to check

Skidog214

Thanks, guys.

The alternator instrument light in the dash does not come on when the key is on. I don’t recall if it was coming on before. It definitely did not light up to warn that there was a problem.

I called my mechanic this morning and will be taking the car to him tomorrow. He too mentioned that if the alternator instrument dash light s burned out the alternator won’t charge. So, he said the bulb is the first thing they will check.

Please tell me a little more about wiring in a volt meter. Where do you recommend it be placed?

Thanks again.

theiceman

any switched 12v line will be fine .. i think its yellow.. cant quite remember ... BTW mine always sits around 13.5-14 volts


Attachment 1336153

Skidog214

Very good. Thank you!

theiceman

there are definitely more elegant solutions, some people replace the clock in the dash with a gauge, but mine is just a driver quality car so i needed something functional.

BTW im not one of those poseurs who put their gauges sideways in the dash because i want everyone to think im Walter Rohl. I am only 5',7" so have the seat closer, and i can only see the bottom half of the gauge.

Ironman88

Another solution is to go with an Antigravity Battery Tracker.

Simple install - directly to your battery. Communicates to your phone via a free app provided by Antigravity.

This will provide you with real-time and tracked history of your battery's condition. Also monitors over-charging and under-charging of your system and provides that data in recorded history shown via the app.

Voltage test, cranking testing, and charging testing.

Among other benefits that this unit provides, it helped me conclude that my alternator was not over-charging my battery at any point when driving the car (no chronic or intermittent problem.) The data was available within the app - monitored and recorded during each drive.

Relatively inexpensive - $35 on Amazon.

https://antigravitybatteries.com/dow...ser-Manual.pdf

Skidog214

Love this idea!
Thanks

Antigravity

Thank you for the mention Ironman88, and just to add a little more info to what was mentioned I have some screenshots of the app below showing your real time voltage reading as well as daily grid views where you're able to monitor how fast the battery may be discharging as well as the times when the vehicle is running to ensure it is being charged. When looking at the full day view you can also tap right on the screen to see exactly what the voltage is reading at that point as the images show highlighted in orange. The daily grid view is stored on a rolling 30 day basis so very easy to see how everything is performing over a duration of time. As always please feel free to reach out to us if you have any questions at all.


Best regards,
Chad
chad@antigravitybatteries.com

Batman 357

I have the same tool. What do the bars on the right side mean. My new battery only goes half way up.

mk85911

my guess would be the alternator. There are some diodes that burn out. An electrical shop can probably replace the diodes, which are cheap, and the process is sort of simple to someone with some experience working with electrical items. Otherwise, probably time for a new or rebuilt alternator. In the nearly 38 years that I have owned my 1985 911, I have replaced the alternator three times; seems to be every 12 years like clockwork, which works out to be about 40,000 miles, in my case. Good luck, Mike