[V8] Finding Excessive Battery Draw

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Mon Mar 13 01:49:45 EST 2006

... I got a chance to go over the V8 wiring diagram over the weekend.  I used the 1991 wiring diagram (W42 911 501 160 1).  The goal was to come up with a list of fuses to pull when trying to isolate a battery drain when the car is shut off.  

As I noted in an earlier post, there are only a few circuits which may be enabled when the car is shut down.  In Audi wiring diagram speak, this is primarily the "30" current track.  Removing fuses (and relays in come cases) removes loads from the electrical system, and if you are monitoring the current drawn from the battery while removing loads you can isolate what load is discharging the battery over time as the car sits.  Here's a list of what I found:

S2 - Emergency flasher circuit
S3 - Brake light/horn
S4 - Most accessories (like radio, make sure you have code!)
S19 - Central locking/door lock heaters
S20 - Seat heaters
S21 - Windows/sunroof
S25/S44 - Power seats
S51 - Cell phone

Circuit breakers/Relays
S43/S64 - relay locations 13 & 14 - circuit breakers
J17 - relay location 10 - powers circuits other than fuel pump
J59 - relay location 5 - load reduction relay (supplies "X" track)

Other notes:
Ignition switch supplies current to "15" current track
Headlight switch has circuits which are powered from 30 track
ABS Modulator is connected directly to "30" current track

I'd imagine that these notes may apply to the other model years, and you can use the documentation for your car (owners manual and fuse box covers) to confirm that the fuse to circuit mapping is the same as I listed here ...

Steve B
San José, CA (USA)

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