I am looking at a '90 100 which has an electrical problem. It has had the
alternator replaced by the dealer but still drains the battery in less than
24 hours. Outside of completely rewiring what could be a probable cause?
I've thought about pulling fuses one at a time until the problem ceases but
not sure, without complete schematics, if this would isolate the problem to
Your best plan of action would be to hook up an ammeter to measure current
draw, and then isolate by pulling and replacing fuses where most of the draw
is going. Then, using the Bentley Manual you have bought from
eBay/Audiworld/Audifans/local dealer or borrowed from a local Audi-fan/a
friend's garage/the library/???, you figure out which
relays/accessories/wires are connected to that fuse. That's what the
dealer's mechanics would do......
If the current draw is not very much, you might look towards things like:
- condition of the alternator (/engine) ground
- condition of the splice in the main power running through the firewall and
to the battery
- age and condition of the battery
Before you "completely rewire", which may be accomplished by taking the car
to a wrecker and getting a "completely wired" replacement from the
classifieds, I'd spring for a Bentley Manual.
1987 Audi 5kTQ - Bentley Factory Manual set close at hand
1980 Audi 5k - 2 (Main+redundant second copy) Bentley Manuals on hand,
Haynes and Chilton manuals used to hold Bentley Manual open to correct pages
1962 and '64 Auto Union DKW Junior deLuxes - pre-Bentley Factory Manuals on
hand - in both English and German
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Thanks for the advice. Being an old electronics engineer I am betting on a
ground fault probably in the main power line. I'll take your advice and use
the Bentley over the other manuals - never found them much good. The
battery and alternator are both new. I thought as I'm now retired this car
would let me get back to my hobby of restoring autos to new. Since the
owner only wants 300 for it (and other than the electrical it is in pristine
condition) I figure I can't go wrong.
Didn't I just hear your local Audi parts guy chortle "muhuHAHAHAHA!!!!!" ;-)
I guess they're an OK car to work on - I'm assuming that the car is
non-turbo (they're a bit more complex). Audi does some strange things with
wiring - like how most of the power for the windows, sunroof, mirrors, etc.
goes through the driver's door jamb...twice of course. Over the years, the
opening and closing of the door breaks the wires and causes some weird
behavior. The main power cable, passing along the passenger side (North
America assumed) from the alt to the battery has a heat-shrink encased
splice near the firewall. Years of salty water, antifreeze, oil, etc. the
cable will wick moisture to the splice and disintegrate the connection.
(With the car running, measure the voltage at the jump-start post under the
hood and at the battery - the difference is mostly due to the splice). If
your dash lights ever stop operating, there are 2 common causes: - license
plate bulb light burned out or wrong wattage bulb used or - headlight switch
on column melted internally (DIY preventative maintenance is to build your
own relay harness to switch bulb power). There are some minor circuit board
issues (such as flaky circuit connections on the tachometer leading to
inoperative cruise control)...and some major ones (early 90's Bose equipped
systems with amplified rear speakers can catch fire!) The Bentley Manual
set is always important to have at hand, as well as a review of the
newsgroup archives at:
www.audifans.com - the quattro list is not just for those who own Audi
Quattros, or Audi cars that have quattro systems installed (not the same
www.audiworld.com - look to the Type 44 (100/200/5000/V8) forum
www.sjmautotechnik.com - his troubleshooting section of his web site is
reason enough to patronize his Audi Parts business
Of course, I believe that Lucas-equipped vehicles hold the crown for
electrical issues - not that I've had experience with that, though my mom's
MGB would start by pulling up on the handbrake. lol
There's lots of help here on the net, feel free to join the collective.
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
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This should be a good hobby car for you. Very rewarding to get one of these in
good running shape and very doable.
Steve's recommendations are, of course, right-on. I would like to add a couple
of guesses / hints.
Have your battery load tested to find if it has a shorting cell.
There are two places that are very likely to be the source of the problem.
- The wires break and short at the driver's side where they enter the trunk
hinge due to flexing.
- The wire bundle that runs from the drivers side kick panel, through a rubber
accordion like tube and into the drivers door always get broken wires the affect
many things in addition to causing current draw.
Get out you solder gun with rosin core, heat shrink tubing and some crimps. Try
to find 18 or 20 gage marine wire because it is pre-tined and has more strands
to withstand future flexing.
former - four T44s. Last one was '91 100q
current 98.5 A4 1.8TQM
The Murdock's wrote:
Rewiring is only an option if the wiring is burned.
Pull one fuse at a time and measure if there is any current flowing in the
individual circuits, there is a fuse list on the fuse cover, some of the
fuse circuits may have a small current, but anything over 100 mA indicates
I have seen a similar problem caused by a defective boot lamp switch.
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