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Thread: Wiring Harness Questions

  1. #1

    Default Wiring Harness Questions

    I have a 1976 Mustang with a stock 302 that I'm in the process of converting to the Avenger EFI system. Mostly I have to say it's a great system that's very straight forward but I'm a little hesitant on a couple of the connections called for. First of all, my tachometer input wire. It's the loose yellow wire on the harness. From what I understand I should be able to hook it into the negative side of my coil for it to function properly. Is this correct or do I have to do more digging on the type of ignition system that was in these cars back in 1976? On that same note, am I able to connect the switched power, red/white striped wire, to the positive side of the coil? I know that in general these should work but the last thing I want to do is fry my ECU or my engine due to a simple wiring malfunction.

    I'm also looking into purchasing the oil and fuel pressure transducers.
    I located them in the Holley store but I'm not sure on where I would install them onto my engine.
    Otherwise my install has gone very well and hopefully it will be running by next weekend

  2. #2
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    Quote Originally Posted by AdamRobinsonnn View Post
    First of all, my tachometer input wire. It's the loose yellow wire on the harness. From what I understand I should be able to hook it into the negative side of my coil for it to function properly.
    Before this question can be answered, I need to know what your ignition system consists of. Is this an ECU controlled timing application?
    The "loose" yellow wire (from the main harness) is used without a CD ignition box and when not controlling timing (with the ECU).

    On that same note, am I able to connect the switched power, red/white striped wire, to the positive side of the coil?
    I wouldn't do that, it's not a clean 12V source.
    Some older ignitions even had a ballast resistor in the coil wiring (<12V).
    I would connect directly to a keyed 12V wire from the ignition switch.

    I'm also looking into purchasing the oil and fuel pressure transducers.
    I located them in the Holley store but I'm not sure on where I would install them onto my engine.
    The EFI main harness is already wired (with labeled connectors) for the oil & fuel pressure transducers (plug & play).
    The oil & fuel pressure transducers are used for Data Monitoring, Data Logging and setup Outputs based on oil & fuel pressure.
    I installed the oil pressure transducer at the rear of the engine block with the OEM oil pressure sending unit.
    I installed the fuel pressure transducer on the remote mounted fuel pressure regulator's gauge port (MPFI).
    http://forums.holley.com/showthread....2756#post32756 (Related Forum Thread)
    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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    Well I have just a stock set up, the Motorcraft distributor, stock ignition coil and my system also has an ignition module Motorcraft part #12A199. Hopefully this helps.

    Thanks for the info on the other connections. I think I've got them figured out and the two transducers ordered, just struggling on that last wire.

  4. #4
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    Quote Originally Posted by AdamRobinsonnn View Post
    Well I have just a stock set up, the Motorcraft distributor, stock ignition coil and my system also has an ignition module Motorcraft part #12A199. Hopefully this helps.
    So this isn't an ECU controlled timing application and no CD ignition box.
    In which case, you will use the yellow wire (not yellow/black wire) for the RPM input signal.
    This loose yellow wire will connect to the negative side of the ignition coil.
    http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual - page 15)
    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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    Thank you very much for the help Danny.
    Last thing that I'm a bit hesitant before finally cranking my engine is, I couldn't find a very good switched power source.
    So I ran a relay from the positive side of the coil to the red/white wire, so it will activate whenever there is power to the coil but still get a full 12 volts. Is this correct or should I keep searching for a better source?

  6. #6
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    Quote Originally Posted by AdamRobinsonnn View Post
    So I ran a relay from the positive side of the coil to the red/white wire, so it will activate whenever there is power to the coil but still get a full 12 volts.
    That works, however, if anything ever goes wrong with that relay, the engine dies without warning.
    I wouldn't add a potential failure item. The ignition switch must have a wire that's powered in "run" and "crank" key positions.
    Furthermore, since your ECU is probably mounted inside the vehicle, connecting to the ignition switch should be easier.
    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.

  7. #7

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    Unfortunately, I haven't been able to locate a good wire for switched power. I've tried getting under the dash and find anything as well as under the hood but with very little luck, especially since I can't crank the engine without this wire attached. Do you have any insight on what I need to be looking for? Color? Location perhaps? I know this is a long shot as all vehicles are different, but finding this has proven to be a challenge.

  8. #8
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    Quote Originally Posted by AdamRobinsonnn View Post
    Do you have any insight on what I need to be looking for? Color? Location perhaps?
    The easiest way to find this wire, is to look at the wiring schematics in a factory shop manual or even a Haynes manual.
    The ignition switch must have a wire that's +12V powered in "run" and "crank" key positions leading to the ignition module. Maybe try the ignition fuse.
    The ignition switch wouldn't be able to start the engine, if there wasn't an ignition circuit that's powered in the "Run" and "Crank" key positions.
    https://www.msdperformance.com/suppo...s/#EngineRunOn (MSD Troubleshooting - Engine Run-On)

    I have a '78 Ford Bronco; this particular wire might be the same color as your '76 Ford Mustang.
    I also have the Holley EFI TSLCD, so I needed two sources that are powered in "run" and "crank" key positions.
    I connected the TSLCD Switched +12V wire to a WHITE wire at the rear of the ignition switch.
    I connected the ECU Switched +12V wire to a BLUE wire in the engine compartment (Carburetor Throttle Emission Control Solenoid).
    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.

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