Bad Battery or Alternator?

[goofycarp]

Help. I charge up the battery and it will take a charge. If I let the car sit overnight without charging, next morning it's dead. The only things that I can tell that are drawing amps are the radio for an internal clock, I guess, and the clock on the dash. Any ideas of what's going on? Battery bad? The battery is an optima, and it's in a '70 911t; should I go back to the 2 battery system or ? Thanks for any ideas; first time owner so pardon the ignorance. Thanks, Cort Chambers.

[pwd72s]

Cort, I'd suggest plugging in a voltmeter...you can make a cheap one by hooking up a cheap multitester to a male cigarette lighter plug. At rest, battery should read above 12V, should drop into the 11's or slightly below while starting, then up to beyond 13V while running. This test will give you info on whether or not your charging system is good. If your battery is good, then you probably have a drain somewhere in your electrical system...but start with testing your alternator and voltage regulator...that's easiest.

[nick-moss]

Cort

Does the battery hold its charge if you disconnect it? If it does then maybe you have a drain to earth somehere which you may track by putting an ammeter across each fuse. Also check that you haven't got an interior light that stays on. I had a 73 911T that switched on the dashboard interior light every time I opened the glovebox.

[BHerrmann]

My glovebox clicks the light on nearly every time I open it. What's happening here? Is the top of the glovebox door bent or warped? Maybe it's the
adjustment on the door itself. It's one of those things I've been putting off checking out. More than once when I first got the car, it drained the battery.

[pwd72s]

Bruce, are you aware that the glovebox light lens is a "rocker switch" itself? I've met people who have owned their cars for years without learning this. It's a 3 position switch, allowing the driver to select always off, on when the door is opened, or on with the door closed for map reading, etc.

[911pcars]

It's either a bad battery or a circuit that's draining the battery.

Charge the battery as recommended, then have an auto electric shop test it. Actually, with new diagnostic testers, a battery can be tested even if it's in a discharged state.

If the battery is good, then it's a "live" circuit that's using up the battery. To identify the circuit, connect an ammeter in series with the negative (ground) cable. The meter will show current flow. If it's greater than around 30-50 milliamps, there is a parasitic current drain. Disconnect one fuse at a time and see if you can isolate the circuit(s) controlled by this fuse. Once identified, you'll need a wiring diagram to trace the circuit. Try to isolate parts of this circuit to determine what's causing the excessive current draw (short circuit, faulty load, etc.)

Hope this helps,
Sherwood

[BHerrmann]

Paul, I've noticed the rocker switch part but what happens on mine is this: the off position is closest to the dash-when I open the glovebox, the top of the glovebox door kicks the switch to the always-on position and unless you catch it, it will stay on when you close the glovebox. I'm used to it now but at first it caused a lot of frustration. I'm sure I can fix it, just have to spend the time to get it adjusted properly.

[pwd72s]

Oh yeah...I'm sure that's a trim adjustment of some kind. Evren just sent me a neat set of small digital calipers as a gift. Lemme know if you want any measurements from a still functioning light.

[HarryD]

Paul, I've noticed the rocker switch part but what happens on mine is this: the off position is closest to the dash-when I open the glovebox, the top of the glovebox door kicks the switch to the always-on position and unless you catch it, it will stay on when you close the glovebox. I'm used to it now but at first it caused a lot of frustration. I'm sure I can fix it, just have to spend the time to get it adjusted properly.

I had a similar problem with the light over my glove box. One day, I took a close look, pulled it out, rotated it 180 degrees (so the switch is on the other side) and put it back in. Works great!

There is a three position switch on the light. One postion is "always off", one position is "always on" and the remaining position is "on when you open the glove box".

[BHerrmann]

Thanks for the offer Paul, I think I might try Harry's method, if that works I'm set. Can't see any down-side to having the switch on the other side...
I'll let you know.