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Thread: Solid State Relays

  1. #1

    Default Solid State Relays

    I've read a few posts where SST relays are used in place of the standard relays. I've searched around and some cannot be ground triggered. I want to use them for my fan relays. Anyone on the forum have experience with a SST relay that can be ground triggered? Also, is the Fuel pump relay also ground triggered off the EFI? Thanks.

  2. #2

    Default

    MSD sells a solid state relay that can be ground triggered. I use the MSD relay in both of my EFI cars. The fuel pump relay in the Sniper wiring harness is ground triggered. The instructions are misleading. The trigger line is a ground signal, the output from the relay is +12 volts.

  3. #3
    Join Date
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    Default

    Every relay I've seen (normal mechanical, or solid state), can be positive or negative triggered. Doesn't matter which side is switched, the relay doesn't know that. Gary
    Regards, Gary

  4. #4

    Default

    Right, relays just need a completed 12VDC circuit to close the relay and allow voltage to pass through. Doesn’t matter if it’s switched on ground or hot for the trigger circuit. However, the I/O of the Sniper is switched negative. So just run a +12VDC to one side of the relay trigger and the Sniper’s I/O to the other side of the relay trigger, then line (battery) and load voltage wires to whatever you’re powering.

  5. #5
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    The electric fan relay doesn't need to be a solid state relay. A good 75+ amp (diode protected) relay will provide many years of service. I've been using the same one (illustrated in this LINK) for almost ten years.

    Yes, some specialized solid state relays are only +12V or Ground triggered. Example: The Holley EFI 554-111 SSR/Solenoid Driver can only be Ground triggered.
    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/3000 RPM converter, FPP aluminum driveshaft, FPP 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 & MT 245/45R17 tires.

  6. #6

    Default

    Thank You everyone. I have my fans connected with a mechanical relay, but had a bit of run-on when I shut off the engine. I read on this forum that the diode or SST relays might avoid that issue. I read somewhere, during my Google searches, that some SST relay (not mechanical) needed to be positive triggered. I interpreted that (or misinterpreted) as not being able to be negative (ground) triggered. I like the diode protected option, so I think I will go that route. Again, thank you all for your quick and informative responses!

  7. #7
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    Default

    If you're getting engine run-on, do some research on putting a diode on the alternator trigger as well.

  8. #8
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    https://www.msdperformance.com/suppo...s/#EngineRunOn (MSD Troubleshooting - Engine Run-On)
    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/3000 RPM converter, FPP aluminum driveshaft, FPP 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 & MT 245/45R17 tires.

  9. #9

    Default

    Thanks Danny. I saw that when I was searching the forum. I don't have an MSD box and I'm using a 1-wire alternator. I found some diode protected relays that can be used in my existing holders, so I'll try those first.

  10. #10
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    You're welcome.
    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/3000 RPM converter, FPP aluminum driveshaft, FPP 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 & MT 245/45R17 tires.

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