Electrical gremlin killing batteries and my Fun

[dyten]

Hello, I have more battery problems with my 1986 911.
For the past 2-3 years I've put 6 new batteries in the car. The last battery was sitting, new, in the car for 5 weeks without being driven, and it's now dead. It was never used.
Now we took out the alternator because that seemed to be where the drain was coming from. A shop specializing in rebuilding the part just called tonight and told us the alternator is fine. So we're off looking again.
My dad, who is an electrician, and part time car guy/ handy man, tested the fuses using a digital multimeter. The fuses that were still live when the car was off were numbers 2, 3, 4, 5. I forgo to write down how much draw was coming off of the battery from the fuses, so I'll have to try and find out again this weekend.
The big cable from the battery is the only one showing a draw. We thought it was the alternator that was the problem, but we just got it tested, and it's still fine (and since the regulator is part of the alternator it should be fine too??). What is on main big cable from the battery on a 1986 911 besides the alternator and the starter? Could a starter be draining the power? Does the 86 have a computer that can be causing a draw?

-We checked all the lights and they are either off or the bulbs are absent.
-Alternator is fine.
-No alarm ( I don't think as I've never activated one, did they come in the 86s?)
-Simple stereo.
-A previous owner had a navigation system in the car, but I think all the equipment is gone.
-Once the car is running it goes perfectly until turned off.
-Clock and the light bulbs setting to turn on when the doors open don't work

I really need the electrical diagrams to help trace down the problem, but the shops that I've tried online don't let me enter my non USA Visa number. The ones on this web site only go up to 1982: http://www.pelicanparts.com/911/911_Parts/911_electrical_diagrams.htm Would the 82 diagrams be similar enough to an 86?

I've had this car 2+ years, and have had nothing but headaches with this battery thing. I don't have the confidence to take it on long trips because I've been needing boosts so often. I can't afford to take this to a garage where they charge $70 an hour to poke around and find a problem that seems to be hiding under lots of hours of work. Recently I had to shyly ask a family of five jammed into a little old rusted hatchback for a boost to my 'luxury sports car'.
Any help would be so appreciated. I'd love to be able to finally enjoy this car as I should. it's already June and I still haven't had it out yet!!
Thanks,
PS

[svandamme]

some fuses are always live, regardless of the contact on/off
hazard lights
indicators have some parts wired for parking light
the main and taillights have some parts wired for parking light too
then there's the cabine light, if you open your door...
the clock
glove compartment light
luggage compartment light
the horn
modern radio's have a direct feed to to save presets

not sure if there are others


82 would not be similar to 86, because 86 had EFI Motronic, and 82 was CIS Kjectronic , whole different injection system


as a workaround, to get you some sort of battery protection, you could look in to this

http://www.noflatbatteries.com/
not that expensive, and it will save your battery from draining, did the same on my 924 some time ago, it does work, but it's not a real fix

[dyten]

I was thinking about the battery cut off, but then I have to reset everything all the time. That said, the time of day is not as precious as finally getting to drive the car without worrying.

[rgdalacrity]

Please check to see if your window still goes up and down when you open your door after you shut off the ignition. If it does still go up and down, pull on the little door light switch located in the door jam and this will shut down the current going to the window and thus solve the drain problem. Now it is time to change the light switch in the door jam.

[dyten]

Unfortunately it's not the door switch. I wish it were.

[svandamme]

could put an amp meter on the fuse block to find out where it draws current.... pull the fuse, and put the meter on the 2 poles, should then see where it draws the most...

[Tyson Schmidt]

The '86's have a relay that keeps the power windows activated until the doors are opened. if the door contacts that turn on the interior lights never make contact, then the relay for the windows will stay on all the time.

The stereo is also a likely suspect. I've seen an otherwise perfectly ggod stereo that was drawing .5 amps just sitting there. It draws straight from the battery for the memory. Usually a yellow wire.

The resting amperage draw for your car should be in the .025-.035 range. Remember that zero after the decimal point.

[dyten]

One wire goes int the starter then becomes two wires which lead the alternator/regulator. They continue on somewhere after that, does anyone know where the wires go on an 86? They aren't shown on the 82 electrical diagrams we've been looking at.

The Motronic/ Kjectronic that Svandamme mentiones shouldn't have any relation to wiring from the alternator/regulator, would they?

[911pcars]

As svandamme and tyson point out, it sounds like a parasitic current draw.

Measuring source voltage at a fuse (or battery terminal) is not measuring electricity usage, just voltage potential - not the same. Assuming the battery isn't dead, it or any circuit connected to it should always have source voltage (~12 V). Current flow, however, is controlled by a circuit switch operating a load (e.g. light bulb, motor, etc.).

In the case of a faulty relay, the internal contacts can stick together and create a current draw which will discharge the battery. A partial or intermittent short circuit will also draw current from the battery regardless of the status of the switch.

I suggest performing a search in the archives under "parasitic current draw" for details touched upon by svandamme's response.

Specific circuits suggested by some to inspect are merely common trouble areas for certain MY vehicles. A basic troubleshooting procedure should result in a more accurate assessment of the offending circuit and less parts replacement costs.

Sherwood

[Mitch Leland]

Howdy,

I replaced my battery recently due to what I thought was a bad battery, even the parts house agreed. It turned out that the trunk light wasn't going off. I had the right lens, but the bulb holder was incorrect. I'm sure you problem is not that simple, but I thought I would just mention it anyway.

See ya,

[dyten]

Sorry, 911pcars I don't understand what you mean?
-Specific circuits suggested by some to inspect are merely common trouble areas for certain MY vehicles. A basic troubleshooting procedure should result in a more accurate assessment of the offending circuit and less parts replacement costs.

Of course I hope it's not too expensive to fix, but if it is, I'm definitely willing to pay what is needed.

The battery is definitely dead, that is (right now) my only sure bet. It's a new battery, and after six weeks it's very dead (to the extent that it won't hold a charge anymore).

I've checked all the threads with the heading "battery drain" "electrical problem," "wiring issues" and many more. I just haven't been able to fine any info which has lead to a fix. I've been trying for a while now.

the mechanic told me that there is nothing wrong with my car, yet I've just lost another battery. Taking it to a mechanic seems problematic now since the two that have so far looked at it told me the car is fine.

[ChrisBennet]

If you are going to maintain your car yourself you really need to get the Bentley Carrera manual. It has the wiring diagram for your car among other things. Next you need to invest in a meter that can measures amps if yours doesn't.

Here's the basic plan:
1. Turn off car. At no time during this test should you start the car - you can hurt your meter or blow it's internal fuse.

2. Disable the trunk light either by taping the pin switch closed or disconnecting it.

3. Measure current draw by disconnect the the positive (+) battery cable and place the meter (in AMPS mode) between the positive battery post and the disconnected cable. Be careful not to let the cable touch anything while it's connected to your meter.
Typical draw is less than .045 amps or 450milliamps ("450ma").Edit: Oops I mean 45ma. Nothing like being an order of magnitude off...

4. If this looks OK you may have an intermittent problem which is why your mechanic couldn't find it. You will need to try to make the drain happen so you can "catch it in the act".

5. If you have a drain great than you should, you can pull each fuse one at a time and see if the drain goes away (time consuming). I'd look on the positive battery cable connector specifically at the wires fastened to the side of the connector. I'd unfasten them and see which one has the draw and then look at the wiring diagram and see what it goes to.

The last time I had to track down something like this the culprit turned out to be a non-working factory clock. The clock is one of those things that is always "connected". I've never seen or heard of a clock doing that before (but I don't get out much either).

Note: When you have the connectors apart, this would be a good time to clean them up using a metal "toothbrush" or some fine sandpaper. Get a can of electrical contact cleaner and spray it on the connectors. I wipe a little vaseline or silicone grease ("Silglide") on the connects before reassembly to keep oxygen away from the surface.

hope that helps some,
-Chris

[Wil Ferch]

What Chris Said...nice elaboration on a test procedure.

BTW...spec "standby" draw for an 86-era 911 is more like 16-18 mA ( milliamps).

- Wil

[dyten]

Thanks Chris, I'm going to follow your guide exactly and see what I find.
I also have a clock which isn't working, I wonder if that could be my problem??

[Tyson Schmidt]

Hey, you're right Wil. I think I gave the 964 value on the amperage draw.

[911pcars]

"Sorry, 911pcars I don't understand what you mean?
-Specific circuits suggested by some to inspect are merely common trouble areas"

Dyten,
What I meant was to look at the big picture instead of concentrating to much on the anecdotal examples provided by various owners. By all means, inspect the easy-to-access circuits and accessories, but first establish there is a current drain with the proper meter and avoid the temptation to replace parts based on a hunch and the relative low cost of a part. For example, battery shops are full of pre-owned batteries that still have life in them. Why? Because many owners think or assume a discharged battery is the source of their electrical malfunction, and they replace it with another and begin the whole process again.

Chris kindly described the procedure to measure parasitic current drain. There are additional conditions that prevent electricity from moving from point A to point B. There's more in the archives in case you care to look, but start with the current drain test and let us know how it went.

Sherwood