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Car Forum / Audi Cars / January 2006AUDI 100 Electrical Problem
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 a system. Hello Murdock's, 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. Cheers! Steve Sears 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 while working 1962 and '64 Auto Union DKW Junior deLuxes - pre-Bentley Factory Manuals on hand - in both English and German (SPAM Blocker NOTE: Remove SHOES to reply) >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 >a system. 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. > Hello Murdock's, > Your best plan of action would be to hook up an ammeter to measure current [quoted text clipped - 28 lines] >>ceases but not sure, without complete schematics, if this would isolate >>the problem to a system. >8------SNIP------8< 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 thing, necessarily) www.audiworld.com - look to the Type 44 (100/200/5000/V8) forum also: 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. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply) 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. Have fun. TonyJ former - four T44s. Last one was '91 100q current 98.5 A4 1.8TQM > 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 [quoted text clipped - 36 lines] >>>ceases but not sure, without complete schematics, if this would isolate >>>the problem to a system. >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 >a system. 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 an error. I have seen a similar problem caused by a defective boot lamp switch. Greetings Aksel |
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