Easy electrical question (if thats possible)
 

In my stock 89 carrera, how many wires should be connected to the positive terminal on the battery? I've got a couple, but do not know exactly where they go aside from the starter.

Six, according to page # 970-11 of our Bentley,

As many as you want.

You're right, that was easy.

I am currently experiencing some parasitic drain. Trying to isolate the problem by removing fuses has not been productive.

I currently have four cables at the positive terminal.
One big one going to the starter that was recently replaced.
Two smaller red ones that are bundled together in what appears to be OEM harness.
And one smaller red one, approximately 18 gauge.

Thoughts?

Just put the meter between the ground wire and the ground terminal. It will show the drain. Then remove the wires on the positive side one at a time. When the drain goes away you know which wire it is. Trace that wire and repair the drain. Easy.

Drain will be shown in milliAmps (BTW),..as we're assuming you've used a meter in this protocol before.....just checkin' bro'.


Not quite clear on "why" it wasn't "productive"?

Best,

Doyle

Justin,
There are several circuits in our cars that connect directly to the battery such as the starter, or to the wiring harness via Terminal 30 such as one side of the fuel pump wiring, the ignition key, clock, radio settings, alarm, demobilizer, and at least on control unit on my car.

Pulling all the fuses will not stop the drain from these systems. GH85 had it right; Remove the ignition key and put it in your pocket, FIRST connect the ammeter (on the 10 AMP scale) between a good ground and the battery - (negative) post. THEN remove the ground wire from the battery (this way you don't lose your clock or radio settings) and note the reading. It should be very low, maybe 10 milliamps (or .01 AMP max), you may have to adjust your scale downward to read it.

If it is not low, you will need to isolate the circuits. A quick way to do this is disconnect one wire at a time from the positive side of the battery. The fat one goes to the starter but that is an unlikely source because the solenoid must be engaged to conduct battery voltage to the starter. The second smaller red wire will go to the fuse box or "central electrics", any other wires on the positive side are suspect until you clear them as having no current flow.

If you still have current drain, then do this. Remove all the fuses and label all the relays prior to pulling them out, then check your current drain. If it is zero, just replace the fuses and then the relays until current flows and note the value. If you find a large current drain, you have found your problem. If not, you have a bad ignition switch or something else on terminal 30 (unfused power). For that you will need a model-specific wiring diagram to discover and locate all the harness plugs that supply terminal 30 current in the car. Disconnecting the harness plugs or jacks on the electrical part will certainly show the current drain as the current has no where else to go except maybe a wire that is shorting to ground. But that is usually a more spectacular event. In any case you will find it if you chase the harness hand over hand.


Good Luck,
Mark

lucittm - forgive my misunderstanding but I can't nail down paragraph #2. Specifically, "Remove the ground wire from the battery" Is that the big fat ground wire from the negative terminal? My layman's thinking says if you kill the ground then the radio and clock die. What am I missing? Does that ammeter carry the voltage then? Thanks - just seeking clarification for understanding this procedure.

Answer
 

You'll still have a complete circuit as the ammeter is now in series and thus completes circuit. The heavy ground cable is now redundant.
On a multi-meter, on the voltage function there is no current passing through the meter,
With the ammeter function, the meter is actually inserted into the circuit. That is why you have to move lead to different receptacle. And also why it is usually fused.

Cool! Thank you. I always wondered why you could read a 220 volt circuit and not have the MM melt in your hand.

Thanks guys, lots of help here. I was definitely getting some drain from my radio/interior lights/clock fuse. I am not sure why, but have since removed it to diagnose further drainage.

With my ammeter in line with the negative battery post and the car's ground cable I get a draw of 37.8ma, which doesn't seem like much--but remember the clock is disconnected.

Is this an ok amount?

Lucittim,

I just re-read your post as it is jam packed with info, and now see that 37.8ma is high. I will start at it again tomorrow, as it is now late here.

Also, I possibly made a rookie mistake earlier by removing all the round red relays without labeling them--are they not all the same?

More
 

The memory function of your radio will draw a minute amount. Not sure how much. 37mA sounds high for this function.
I would remove light bulbs from their sockets one at a time. I have seen where a broken filament or the socket itself caused a small path to ground.

Ok, so all the are fuses out. The drain is occurring from a non fused circuit connected directly to the positive battery terminal. There are two red wires originating from what appears to be the OEM harness. They act as a pair, neither by itself draws any current, but together ~36ma. I tried to start the car without connecting them to the battery, and I get nothing. I assume this is the ignition wiring--are faulty contacts in my ignition switch draining my battery?

Justin,
You have come far my friend. I think in your car all the red round relays are the same. In my car I have black, silver, blue, and gray relays that all go with different circuits. Some have a unique pin configuration and some don't. Trying to locate which relay P/N goes where is a lot of research, ask me how I know this...

So with the smaller red wires connected to the battery you have a bit too much current drain. This is the dreaded Terminal 30 and runs through the whole car. But the current will always choose the path of least resistance. Because you have already disconnected the clock, that source of drain is eliminated. I would pull the harness plug on the back of the radio and see if that makes a big difference, which I assume it will not. Next, I would pull the plug on the back of the ignition switch, it is keyed so it only goes on/comes off one way.

If that causes your current draw to decrease you still have some circuits to check because this only narrowed the field. The switch could be bad but let's assume it is good. Here are the things that connect to Terminal 30 in my car, yours may be different (here is where you might need a schematic for your car):
Suppressor capacitor
Alternator B+ terminal (could be several pieces in there) Pull the big black wire off the starter to eliminate the alternator and the starter at the same time
Installed telephone
All the fuses in the engine compartment
Headlight switch
Parking lamps (easy to check, just pull the bulbs)
ABS hydraulic unit
ABS relay
Radio antenna booster amp
Buzzer for door open switch (unless you pull the key out)
Ignition relay
Starting valve (pull the plug on this one)
Cold start switch (pull the plug on this one too)
Fuel pump relay
Turbo control unit (Maybe your DME)

If all of these are OK, and there may be more on your car, then I would suspect the ignition switch.

Good Luck,
Mark

Lucittm, Thank you so much for those thoughts.

I checked 80% of the things you just listed but found the culprit to be the following:

Although not a significant drain, there is an unfused red lead coming from the positive battery terminal that controls the power windows.

As you are all aware, different people have varying functionality regarding their power windows with ignition on/off, doors open/closed, key-in and key-out of ignition. This lead apparently draws about 37-40ma at all times in my car.
With this lead removed--I now have only 0.94ma drain, but no power to the windows at any time.

Are my door switches bad? Or is this 37-40ma drain supposed to be constant or what?

See link for details of power window lead:
http://forums.pelicanparts.com/porsche-911-technical-forum/398658-positive-battery-cable-taps.html

Congratulations, you found the mystery current drain. The reading of .94ma is what you were looking for. The circuit for the power windows is a bit complex as you alluded to in your post. I would try to isolate it to driver's side or passenger side first. It could just be a dirty switch or a door closing switch that is not working correctly. Pull the rubber cover of the door switches and see if that makes a difference, they do get stiff. The switches are relatively inexpensive. If you pull the plug off one of the switches and your drain goes away, presto!

Do you have a sunroof, if not, that helps because I would look for a bad motor or sunroof control switch.

Mark

Get those door switches out of there!!!!!!!!!!!!! Pronto! Are they old? then , out they go, irregardless.


Best,

Doyle