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Thread: Fan #2 Output not providing a solid ground.

  1. #1

    Default Fan #2 Output not providing a solid ground.

    I'm just finishing up everything on my Sniper EFI install. The unit runs well, especially after I setup my Dual Sync Distributor to control the timing. The last step was to wire up the electric fans to be controlled by the Sniper EFI unit, as the Sniper CTS sensor replaced where my temperature controlled switch for the fans was before.

    I setup all my wiring, double checked all grounds, that the fans were working, relay working, etc. I wired in a diode as suggested in some other threads. I hooked everything up and brought the engine up to temp, but no fan on! The monitor says "Fan #2: On". I pulled apart the circuit, and used a continuity meter to check the ground coming straight from the Sniper EFI harness. Not a good ground. When checking with a voltmeter, the voltage jumps around from 0 - 12 volts when using the #2 Fan as a ground for the Sniper EFI (the engine is up to temp showing "Fan #2 On").

    Just wondering if anyone has encountered this issue? Also, can anyone confirm that Pin C in the 10 pin harness is the pin for Fan #1? I pulled all the unused wires from the 10 pin, and just ended up using Fan #2 as the green wiring matched up to what I was using. Any help would be appreciated, thanks!

  2. #2
    Join Date
    Dec 2017
    Hollister, CA


    Couple of thoughts here. First of all, yes - the C pin is for the output #1 ground trigger. It has a light blue wire inserted from the factory. The D pin is for output #2 ground trigger which has a light green wire inserted. This is according to page 18 of the installation manual.
    If I understand your correctly, you're not using the C pin - output #1, but are using the D pin and controlling your fan relay with output #2. Is that how you have configured your setup? If so, have you tweaked the output settings trigger ranges as depicted on page 52 of the manual, but swapped the output #1 & #2 values? It's possible that some of the ranges may be conflicting and perhaps the ECU is confused. This is a guess and not likely, but perhaps output #1 needs to be closed before output #2 can be used. IE. logic priority. To test that theory, perhaps move pin D to pin C location and reset your output values accordingly. Like I said, not likely but worth a shot.

    As far as the diode, some diodes have an impedance that may be conflicting with the output trigger in the ECU. Can you verify that the diode is installed with the correct polarity? That will for sure make a difference. I would consider jumping the diode for testing purposed, until you get this issue sorted out. Good luck and please report back. I haven't hooked up my output relay yet, and I'm curious about your findings. Kevin

  3. #3


    I swapped the fan wiring to the Fan #1 output wire, and set the on & off temps where I wanted them. This sorted out my issue! I believe you're correct in that the Fan #1 needs to be on before Fan #2 will be triggered. Odd that it would show Fan #2 on in the readout. Either that, or there's an issue with the Fan #2 pin in the harness. I left the diode out for now, as I will have to wire one in later.

    Just out of curiosity, is there any way to change the Pin Map of the 10-pin harness without a laptop and the $50 USB wire on the Holley Sniper EFI? I would love to use some of the other pins as outputs for some LEDs, etc.

  4. #4
    Join Date
    Dec 2009


    Quote Originally Posted by eightballworld View Post
    This sorted out my issue! I believe you're correct in that the Fan #1 needs to be on before Fan #2 will be triggered.
    Yes, they operate in numerical succession.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

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