Strange Battery Drain

[hah3 at mindspring.com]

This isn't covered in the Bentley, but you might try this link to see if "d=
rawing 12V" makes sense: http://www.tonmeister.ca/main/textbook/electronics=
/02.html
Basically, Volts are a unit of electromotive force similar to water/air/etc=
. pressure. Just because you have pressure doesn't mean you have flow. Flow=
 in electrical circuits is measured in Amperes or Amps for short, and in or=
der for there to be current flow the resistance (think of this as the size =
of a water pipe) must be less than infinity (infinity =3D no flow). These p=
roperties of electricity are in fact related by Ohm's Law (the unit of resi=
stance was named after him) which is: voltage =3D current * resistance or V=
 =3D IR.

Now with that out of the way, what you need to be looking for to diagnose a=
 battery that is not starting the car after sitting for a while is a *curre=
nt* drain, measured with the "amps" setting of your multimeter. You would d=
o this by carefully in a well-ventilated area removing the fat red wire fro=
m the positive terminal and by placing the ammeter in series (between) the =
red wire and positive terminal to see if there is in fact a significant cur=
rent drain. Something in the tens to about a hundred milliamps is probably =
acceptable (running clocks and keeping ECU memory alive); a few hundred or =
more (trunk light stuck on or relay failing) will drain the battery fairly =
quickly. Note that many meters have separate terminals for the 10A range an=
d the 500mA range, start testing with the 10A circuit if applicable. If the=
re is a current drain, one way to isolate it is to start pulling fuses unti=
l it stops draining/drops significantly.

HTH
Henry Harper
http://www.mindspring.com/~hah3  hah at alumni.rice.edu
1991 200 quattro, 114k
1988 GTI 16v, 224k
1992 BSEE w/CS, Rice U

"Arthur, Keith" <Arthur_K at students.lynchburg.edu> wrote:
> Hello,

My 1991 90 is acting up and I was dumb enough to leave the Bentley at
school.  The fat red wire that is bolted onto the top of the positive
terminal with a 10mm bolt is drawing 12V's with the ignition off.  I guess
this either goes to the starter or alternator.  Could someone confirm which
it goes too and what could cause this voltage drain?

Thanks,
Keith