Electrical fault - gurus needed please

[vince_aust]

Gents - having a strange electrical fault where the battery load is 5 amps with ignition turned off

Background

Removed engine for a top end rebuild and a respray at same time - so car has been in bits for 8 months

Problem:

Car completely back together and testing everything before the actual engine start. All electrical systems appear to work with the exception of remote fob ( lock and unlock) but central lock on console works OK. thought I leave remote lock problem till later and then I noticed battery is draining with ignition off??

Diagnose process:

Measured current drain once connected - equaled 5 amps which is a significant draw and I'm not blowing any fuses?
Removed every fuse (one by one - at main fuse block and auxiliary block in engine bay) - still drawing 5 amps?

Interesting point of note is that every time I connect battery current draw increases to approx 8 amps and front and rear indicators lamps turn on for about 1 sec

Could any one possibly shed some light or propose some ideas or directions to check?

[pete3799]

Just a guess........have an alarm system?

[lemonlib]

do you have one of those ancient alarm system with a lock and key? but it should not drain that much..take out the module and jump #61 on the wire side. or is it #64. see if that helps

[86 911 Targa]

Vince,

5A is a very heavy draw, which seems exessive for your alarm system
as it would drain your battery in <24 hours.

Try this to dis-engage the alarm, or pull the connector:



Good luck,

Gerry

[rick-l]

You should add your car to your signature.

edit: what year

[vince_aust]

Gents - thanks for the replies - some good points raised

1. I have a after market alarm system which I have disconnected as part of the diagnosis but maybe the original module still exists - where is this module mounted?
2. I have updated my signature to reflect the car I have - 1987 widebody

[86 911 Targa]

Originally Posted by vince_aust

Gents - thanks for the replies - some good points raised

1. I have a after market alarm system which I have disconnected as part of the diagnosis but maybe the original module still exists - where is this module mounted?
2. I have updated my signature to reflect the car I have - 1987 widebody

Vince,

The factory alarm is buried behind the fresh air plenum in the boot at centerline to the dash
next to the wiper intermittent relay.

But, before you go there, here is the wiring for the factory alarm.

Note that the alarm module is wired directly from the buss (top) of fuse #7,
as opposed to the Bentley.

However, I still believe that your 5A draw exceeds the alarm module draw
in a non-active state.

Therefore, I suggest that your issue lies elsewhere.

Did you have this issue prior to the recent work?






Cheers,

Gerry

[Jim Smolka]

Also a good idea to verify the current reading Amp meter first.

Take a 10 ohm resister on a measured 12 volt battery. See if the current reading shows 1.2 amps. Note: the resister will get hot.

[vince_aust]

Thanks Jerry for the wiring diagram - mine are poor quality.

One of the items I will be testing tonight is the feeds coming off the active side of the battery. My tests to date really involved noting the current draw as i removed the fuses. I have noted apart from the main feed to the starter motor there are two other connection to the active side of the battery. I assume one of these would be to the fuse block. It is also possible that the original alarm module still is installed but not used.


Jim thanks for your note on current draw - Im happy with the accuracy of my digital meter as the high current draw correlated with the time line to completely flatten the battery and I use it to calibrate/test instruments on a regular basis. The resistor idea is a good one but most people do not have high wattage resistors in the tool box. Most of mine would only be 1/4W - the days when I owned a decade resistor box are many years in the past.

[vince_aust]

Guys I think it the starter motor - damm it's a PIA to remove. Have to drop motor just when I finished installing it

Tracked the 5amps draw directly from battery to starter motor - removed main cable from motor and 5a draw gone - I tested this on a bench before I installed, I even opened it up and checked bearings and brushes

[T77911S]

did u remove the cable to the alt first?

trying to think how the starter could draw current, unless something else is connected to the same terminal as the battery

[86 911 Targa]

Originally Posted by vince_aust

Guys I think it the starter motor - damm it's a PIA to remove. Have to drop motor just when I finished installing it

Tracked the 5amps draw directly from battery to starter motor - removed main cable from motor and 5a draw gone - I tested this on a bench before I installed, I even opened it up and checked bearings and brushes

Vince,

Here's the alternator CKT.

Let's verify the wiring/connections/color codes before you drop the motor.

If the issue was not present prior to your work,
it's always a good idea to re-trace your steps when trouble-shooting.

Gerry

[uwanna]

Originally Posted by vince_aust

Guys I think it the starter motor - damm it's a PIA to remove. Have to drop motor just when I finished installing it

Tracked the 5amps draw directly from battery to starter motor - removed main cable from motor and 5a draw gone - I tested this on a bench before I installed, I even opened it up and checked bearings and brushes

You stated when you removed the cable from the battery to the starter your short disappeared. On that starter terminal #30 you also have a wire that goes to the B+ connection on the alternator. My guess is a shorted B+ connection at the alternator or more likely a shorted diode inside the alternator. A shorted alternator diode is a very common cause of a dead battery.

[JJ 911SC]

Originally Posted by vince_aust

... Have to drop motor just when I finished installing it...

Put the car on a lift and should be no problem to remove/replace it.

I replace mine (86) with a Hi-torque one in less then 30 minute on a scissor lift.

[vince_aust]

The 5 amp draw is present when there is only the cable from battery to motor connected. This can only occur if there is a low resistance connection within the starter solenoid (ie faulty solenoid). This was the last thing I checked before I reassembled the starter motor but I only checked it worked (ie throw out action) I never checked any current leakage. I assuming when I reassembled I did something wrong - maybe some dirt or carbon tracking.

Being that I have G50 transmission the upper bolt is not accessible till transmission is dropped about 15 cm. my reading Bentley tells me I do not have to actually drop motor but I have to remove sway bar, accelerator cable and transmission mounts along with disconnection of coupling. Annoying but probably only and hours work I guess.

The last check I guess I can do is remove cable between solenoid and actual starter motor to determine/eliminate fault to solenoid or motor

Thanks for everyone's help

[T77911S]

a solenoid is like a big switch. think about your light switch in your house. when it is off, it is open and no current flows.
a solenoid has a big "plate" for a contact that is pushed up against the 2 big lugs. one has battery on it and the the other is connected to the motor.

you can remove the rear of the solenoid and clean the contacts. this can double the life of a starter. do a search for my thread on rebuiding the solenoid and starter.

[vince_aust]

Gents I found the problem and it was a stupid mistake!!

When I tested starter motor after installing new brushes and cleanup I then pulled it apart and painted the housing. When I reassembled motor I installed solenoid backwards and obviously did not do a final test. The 5 amp leakage was because I was connected direct to the coils of the starter motor. I simply rotated solenoid 180 degrees and it fixed the problem

Thanks for everyone's help

PS: removing the starter motor when engine is installed is a BUGGER of a job

[86 911 Targa]

Originally Posted by vince_aust

Gents I found the problem and it was a stupid mistake!!

When I tested starter motor after installing new brushes and cleanup I then pulled it apart and painted the housing. When I reassembled motor I installed solenoid backwards and obviously did not do a final test. The 5 amp leakage was because I was connected direct to the coils of the starter motor. I simply rotated solenoid 180 degrees and it fixed the problem

Thanks for everyone's help

PS: removing the starter motor when engine is installed is a BUGGER of a job

Problem solved.

Pour yourself a tall one and jump in!!

Good luck,

Gerry

[JJ 911SC]

Originally Posted by vince_aust

...
PS: removing the starter motor when engine is installed is a BUGGER of a job

Build character

Now go for a drive and have fun

[T77911S]

Originally Posted by vince_aust

Gents I found the problem and it was a stupid mistake!!

When I tested starter motor after installing new brushes and cleanup I then pulled it apart and painted the housing. When I reassembled motor I installed solenoid backwards and obviously did not do a final test. The 5 amp leakage was because I was connected direct to the coils of the starter motor. I simply rotated solenoid 180 degrees and it fixed the problem

Thanks for everyone's help

PS: removing the starter motor when engine is installed is a BUGGER of a job

i did not realize you took the starter apart. that would have been good to know.