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Thread: Fox Mustang Tachometer

  1. #1

    Default Fox Mustang Tachometer

    Just completed the install of a HP EFI on my '92 Mustang. I’d like to retain the factory tach, so wondering if I can simply feed it the the coil signal from my MSD 6AL? Stock wiring diagram appears to show the coil (-) driving the tach via A11 (tan with yellow strip). Any help would be greatly appreciated.

  2. #2
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    Read first paragraph: https://forums.holley.com/showthread...464#post100464 (Related Fox Mustang/Holley EFI Forum Post)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

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    Thanks Danny. What’s the difference between A28 feeding the TFI, and the white tach signal wire from the TFI that is feeding my 6AL?

  4. #4
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    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5

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    Tach works using white wire from TFI.

  6. #6

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    Mine (Fox body) also works with green (tach) wire from ignition box. Unfortunately, it reads 20% high, which is annoying. I wonder if it would read more accurately using the Holley pin 28, or if I just have a messed up tach. It's a Digital Dash with LED bars, should be precise.

  7. #7
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    Quote Originally Posted by Cougar5.0 View Post
    I wonder if it would read more accurately using the Holley pin 28...
    It probably would, since that's the Holley EFI tach output wire. Mine works perfectly fine (see post #2).

    It's a Digital Dash with LED bars, should be precise.
    Correct, it's not a Digital Dash problem.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8

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    Hmm, well I tapped into the Holley ignition connector (terminal H) and it works fine. But the reading is the same as using the green "tach" wire from my ignition box. I'm afraid that the tach module is damaged or has somehow been switched to six cylinder mode. I have an extra tach module to compare to, I'll get to the bottom on this one way or the other.

    Edit - apparently Ford was too lazy to calibrate the tach for V6 & V8, oh well.

    https://www.foxtbirdcougarforums.com...?topic=38600.0
    Last edited by Cougar5.0; 11-03-2019 at 05:58 PM.

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