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Discussion Starter · #1 ·
Hello all, I’m a long time lurker first time poster, you guys have unknowingly helped me countless times but this time I can’t find anyone having any similar issue to mine. This has been a long-outstanding issue for me, it’s probably been about 6ish months since I first noticed it but I never got around to digging too deep into it. My 2004 M6 doesn’t have any accessory power when the key’s in accessory mode, nor does it have RAP after the car’s turned off. Everything (radio, windows, mirrors etc) works perfectly when the key is in the on position but as soon as I turn it back to accessory it’s as good as a second off position. I went ahead and did all of my basic checks, the fuses and relays are all good (swapped the ACC relay with various other relays just to make sure), there’s power to the ACC relay when the key’s in accessory mode but no power to any of the accessory related fuses. I pulled the column cover off and inspected the wires by the ignition cylinder, namely the brown/white accessory power wire, and nothing seemed out of place but I couldn’t fit a test lead in to see if there was power there. I also went ahead and checked the BCM wiring harness (which has not rubbed through thankfully) as well as pulled the corresponding connector to make sure the pins for the ACC and RAP were intact. I have a feeling this is gonna result in a fun wire-chasing venture but I decided I’d post up in here first and see if anyone has experienced this before, or if anyone has any other checks I may have missed. Thanks in advance.
 

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Discussion Starter · #5 ·
Well the ignition switch came in today, I swapped it out and everything’s still the exact same. The radio comes on with the key in the on position only, turns off once i turn it back to accessory. I did manage to test both of the brown/white acc wires on the switch connector, and they both have power with the key in the accessory position. I’m kind of at a loss.
 

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this is all from the pdf service manual, which is known to have errors. i'll check on the cd-rom version in a minute.

just a quick look at the 04 wiring diagram, it looks like the BCM provides the ground for the solenoids on both of the accessory relays. the starter switch sends a signal to the BCM as well as the instrument cluster when in the ACC position. wire from the ign sw to the bcm and to the instrument cluster is listed as brown/white.

the two accessory control relays are also in serial, so both would have to work. the wire that grounds the solenoids in the accessory control relays is listed as brown/black. there is also a brown/yellow that provides accessory power to the BCM that is from the front washer/wiper fuse in the instrument panel fuse block.

quite possible the issue could be the BCM or something in the BCM harness. could look at the good old chafing harness problem behind the glovebox and get that out of the way as a possible cause.

will check back a little later to see what the other service manual version i have says.
 

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Discussion Starter · #9 ·
Gotcha, I already gave the bcm wires behind the glovebox and up by the connectors for the bcm a look and didn’t see anything out of line but I’ll give it a closer look. Is there any procedure for checking the bcm as the failure point? (that was kind of my thinking after the switch was a bust.)
 
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