Electrical Issues

BRP83SC · 03-12-2007, 09:35 AM

1983 911 SC

After purchasing the car, I put in a new battery since the previous owner indicated that the battery was 5/6 years old.

Car was starting great for about 6 weeks, then I went to start it and it would turn over slowly, but no start.

I jumped it and it started right up; drove it for a little while; then parked it. next day it would not start--turned over slowly. I did not jump it, but let it sit for a few days. When I attempted to start it again, nothing--battery completely dead.

I jumped it and it started; let it run for little bit; turned it off; attempted to start; turned over slowly but did not start.

I put a meter on the battery prior to jump starting it and it showed it as being drained; after I jumped started it and while it was running, the meter showed the battery at the appropriate level.

I suspect that something is draining the battery so I am planning the "remove the fuse 1 at a time" to see if there is a subsystem drawing on the battery as well as cleaning the gound connections back by the starter, but was wondering if there are any other test and/or procudures that I should consider.

Early_S_Man · 03-12-2007, 10:20 AM

Is your alternator warning lamp working when the ignition switch is on, engine not running? If not, the battery hasn't been getting a charge lately ... it certainly was not recharged during a brief drive!

I suggest charging the battery overnight out of the car, then investigate further.

If the brushes are worn, the charging can be interrupted when contact is lost at the slip rings. There will not be an indication of a problem with the warning lamp!

glenncof · 03-12-2007, 11:08 AM

Sounds like battery not getting charged. When running engine the voltage should be constant ~14.3V. Sounds like the previous owner may have known something was up.

Connect the voltmeter thru cigarette lighter and drive around with headlights on.

I have had regulators go bad/wear-out intergral brushes causing intermittent problems (high and low).

My factory alternator went out at 63K, a rebuilt lasted 98K. If you are handy (and fearless) you can pull it yourself and take to rebuild shop for ~$100. Make sure it's the problem first.

BRP83SC · 03-12-2007, 12:04 PM

glenncof,

Are saying that I can use a cigarett lighter volt meter to ensure that I am getting a constant ~14.3V while driving around with the headlights on?

added information: when the car is idling in the garage; I give it some gas and let up (i.e. done repeatly), the headlight grow brighter and dim as I press and let up on the pedal. Its suddle, but very noticable.

Early_s: When I jump started the car, I let is idle for about 20 minutes, took it for a 20 mile highway drive, then let it idle for another 15 minutes.

I will explore the alternator light

Thanks to both of you for your suggestions and comments--I truly appreciate it.

glenncof · 03-12-2007, 01:18 PM

Lighter is convenient connection in cockpit.

Yea, the voltage regulator is probably gone. My '85 would start with bright lights then dim a bit after 1-2 miles. As you say not much but noticable.

If the voltage is going way up at speed you may be over-charging the battery which will kill a weak cell. Look at the fluid level in battery and for signs of white corrosion on + terminal. Fluid will boil off if over-charge. Black/dark fluid means dead cell to me.

You may want to have Sears or someone check the battery.

BRP83SC · 03-12-2007, 02:25 PM

Actually, the battery is 6 weeks old--just bought it new.

BRP83SC · 03-12-2007, 02:26 PM

Unless I am misunderstanding, where did you get a volt meter for the lighter?

glenncof · 03-12-2007, 02:43 PM

I was suggesting to use lighter as convenient point of contact.

A new battery can take more over-charging before it fails.

Your choices are under-charge, over-charge, or intermittent.

BRP83SC · 03-12-2007, 04:18 PM

got it, the voltage reg is part of the alternator--correct?

I also read about the alternator light which I have not noticed being on; when would the alternator light come on?

glenncof · 03-13-2007, 08:24 AM

Turn ignition key to first position, do not start engine. ALT light should be ON. It will also briefly go on after shutting engine off, during run down.

BRP83SC · 03-15-2007, 07:39 PM

Ok, I charged the battery and purchased a test that specifically provideds a battery reading as well as a Alternator reading (i.e. while the car is running.

BTW, when I turned on the car to the first switch, the battery light came on and when I started the car, the battery lighted shut off.

Once the battery was charged, I fired up the car. The alternator reading was good. Went and put fuel in the car.

Came home parked in the garage and took another alternator reading--still good.

Shut the car off and started it again--alternator is reading OK

Turned it off and hook up a different type of meter (electro-tek); set the DC setting to 50. Hooked it up to the battery, it was reading about 70 on the DC reading.

While still connected, I removed each fuse one at a time. Each time, the reading remained constant.

There is a amp in the trunk area; I removed the fuse from it and the meter remained constant.

I did notice that the positive side of the battery has three (3) smaller wires handing off of it. Did not have time to explore that.

Plus I am not sure it a reading of 70 on the meter is bad.

One more odd thing, when I came home from the gas station and finally shut if off, the horn sounded (i.e. like the sound it makes when you shut off the alarm).