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Old 11-06-2009, 01:02 PM   #1
nitrousdave
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Default Tachometer wire location

Not sure if this is theright spot to post this, but here goes. Since I'm using LS2 coils on my car I need to get the tach working again and to do this I need to find the wire that feeds the signal to the tach. I can't jut use the coil negtve wire because I already used tat wire for the digital ground on the coils and ran it back to the MS2. So does anybody know where the tach wire physically ties into the coil wire? BTW, it's an 85 325E.
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Old 11-06-2009, 01:07 PM   #2
chris325ix
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It doesn't tie into the coil, it's sent from the ECU itself. on the Motronic 1.3 harness it's pin 6, but that doesn't help you. There must be an eta harness chart somewhere, maybe in the engine management forum.
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Old 11-06-2009, 04:19 PM   #3
nitrousdave
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According to the diagram I have the tach is driven from the negative side of the coil which is also the timing control on pin 1 of the stock ECU and this is confirmed by the fact that once I used that wire for the LS2 coils the tach quit working.
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Old 11-06-2009, 04:25 PM   #4
peerless
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On the eta there is a C104 connector that is a 3 wire connector about 3-6" away from the ECM harness. This actually splits out of the loom.

You want the black wire.

Its different on early and late models.
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Old 11-06-2009, 05:26 PM   #5
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Awesome thanks a lot, that will make it easy to wire it to the MS.
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Old 11-07-2009, 09:17 PM   #6
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Got the tach wired up today using the relay method dsecribed on the MS site and it worked, but a relay clicking away several hundred times a minute is very annoying!! So I took the case of the relay and removed the contact andnow its silent and I have a tach again. Thanks, again peerless.
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