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PCM grounding point? (aka head unit ground)

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I'm trying to trace down the root cause of alternator whine / rpm dependent noise in our 996 with PCM (1), and aftermarket amp & crossovers. I've already improved the grounding on the amp (some improvement in whine) and next on my list is the head unit.

Can anyone provide the "correct" grounding of the PCM head unit? Other suggestions would also be appreciated.


PS - newbie member, sorry if this has already been discussed, my search didn't turn up anything addressing this specific problem.

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It is always best to state model and year for this type of question. However, looking at the MY2000 (PCM1) and MY2003 (PCM2) wiring diagrams for the 996 Carrera, the ground connection from the black power plug on the PCM head unit goes to Ground Point 4. I think this is located behind the dash, under the instrument cluster. There are a series of 5 ground points, using M6 studs and nuts, and Ground Point 4 should be the middle one.

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Thanks Richard. 1999 C2 996 with almost entirely aftermarket audio except for stock PCM1 head unit. Other thoughts / suggestions of appropriate ground points to eliminate whine that sounds like it is coming from the gauge cluster & speakers?


Edited by GTRSR
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