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yea i just installed my msd box in today and i went to test drive it and i noticed that my rpm guage isn't working anymore so could i have knocked somethinkg a lose if so wat could i have knocked lose that would have stop my rpm guage from workin ?
 

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INOPERATIVE TACHOMETERS

If your tachometer fails to operate with the MSD installed you may need an MSD Tach Adapter.

Before getting an Adapter, try connecting your tachometer trigger wire to the tach output terminal on the side of the MSD. This output produces a 12 volt, square wave. If the tach still does not operate, you will need a Tach Adapter. There are two Tach Adapters:

PN 8920: If you are using the Magnetic Pickup connector (Green and Violet wires) to trigger the MSD, you will need the PN 8920.

PN 8910: If your tachometer was triggered from the coil negative terminal (voltage trigger) and you are using the White wire to trigger the MSD you will need the PN 8910.

Tach Adapter 8910
Installation Instructions (Adobe Acrobat Reader required)

Tach Adapter 8920
Installation Instructions (Adobe Acrobat Reader required)
 

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The tachometer RPM signal comes from the ground side of the ignition coil. For an '86 model, it should be the Dark Green/Yellow (stripe) wire.
 

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hold on were is the rpm trigger wire at wat does it look like?
fox chassis said
The tachometer RPM signal comes from the ground side of the ignition coil. For an '86 model, it should be the Dark Green/Yellow (stripe) wire.

i have an 87 foxbody, with an msd ignition. i have the 8920 tach adapter but cannot find the wire to connect it to the stock harness. is it the white wire? i tested the green and yellow stripe it did nothing.
any one have an idea where i should look? im trying to use the stock cluster tach hooked to the msd 8920 tach adapter wired through the stock harness.
 

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please let me know if you know where the stock tach wires to the harness.
bump

The Tachometer Trigger is the Green/ yellow wire on the 87. If it didnt work,your gauge is shot, or there is an open in the wiring to the gauge.:bigthumbsup
 
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