LS Harness fuse boxLSX-MS3Pro_injector branch1357MS3Pro-EFI-EMS

MS3-Pro ‘Drop On’ 24x LS Plug and Play Harness w/ ECU

5 out of 5 based on 2 customer ratings
(2 customer reviews)

From: $1,699.00


Injector Style


Alternator Lead Extension – optional

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MicroSquirt CAN Transmission Controller with 4L60E Subharness – optional

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MicroSquirt CAN Transmission Controller with 4L80E Subharness – optional

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Product Description

The MS3-Pro 24x LS Plug and Play Harness is the highest quality, best value option for LS Motors in the industry today.  Save your hard earned time and money while experiencing the virtually limitless feature set of MS3-Pro Engine Management System.  Simply choose your injector style from the drop down menu!

The MS3-Pro LSX Series plug and play harness is professionally engineered and easy to install.  Fire up your engine on day one!   All wiring is composed of TechFlex woven, self-extinguishing wrapped hi-temp TXL & GXL automotive grade wire with OEM Delphi & TE connectors. Reach the battery under the hood or in the trunk with 4 gauge power & 10 gauge ground wires.  All relays and fusing live in a single, waterproof fusebox and the fuel pump wiring / relays / fusing is big enough for pumps that can handle 1000whp or more right out of the box (10ga wire, 30amp circuit).  Additionally, all of the available I/O of the MS3-Pro are brought out in the harness to make expansion as easy as possible regardless of the featureset you’re planning to use, allowing for killer features like traction control, bump box, table switching, flex fuel, and more.  This harness was designed with room to grow!  And did we mention it’s show-quality-drop-dead-gorgeous?

This harness also is designed for optional automatic transmission control using our MicroSquirt transmission controller .  Literally just plug in our transmission controller using the proper sub-harness (for 4L60E or 4L80E) and you’re ready to control your trans!

Required connections:
Constant Power
Constant Ground
Switched Power
Alternator light

Suggested extra connections:
Fuel Pump Power
Tachometer Signal

Note that the alternator connection is designed for high mount alternators such as Corvette and truck setups. Low mount alternator setups such as Camaro, Firebird, CTS-V, and GTO accessory brackets, as well as other aftermarket accessory drives that do not have the alternator high on the driver’s side, require our alternator extension cable.

PLEASE VISIT OUR DOCUMENTATION & DOWNLOADS TABS for complete documentation and base tunes.

*All parts are sold for OFF ROAD RACE-ONLY, ground-vehicle use only. Aftermarket EFI/EMS systems are not for sale or use on pollution controlled vehicles. Alteration of emission related components constitutes tampering under the US EPA guidelines and can lead to substantial fines and penalties. Your state/district may also have specific rules restricting your tampering with your vehicle’s emissions system. In short, as stated before, our official policy has to be RACE or OFFROAD USE-ONLY in ground based vehicles ONLY.

2 reviews for MS3-Pro ‘Drop On’ 24x LS Plug and Play Harness w/ ECU

  1. 5 out of 5


    Ordered the PNP with multec injector clips, it is the nicest drop on harness I’ve seen to date and the customer service, packaging, and detailed instructions are second to none. Hands down would buy again and recommend. Alex Fornal

  2. 5 out of 5


    This is by far and away the nicest, highest quality, most well thought out pnp harness I’ve ever seen or used. Mark Dalquist — Throttle’s Performance.

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For the latest firmware and tuning software, please visit the main download site.
2007 4.8 base tune 1.4.0 (Zip File)
LS1 big cam base tune (Zip File)
Drivers for the USB connection can be found on the FTDI website.

What is in the box?

    • MS3-Pro Standalone EFI Controller
    • LSx drop on wiring harness
    • Fuse block with relays
    • USB and serial communications cables
    • Matching connectors for O2 and transmission / CAN subharness
    • Fuel pump ground wire
    • Includes TunerStudio registration code
    • USB drive (for software / documentation / base maps)

How big is the ECU?

    • The MS3-Pro measures approximately 7" long (including the mounting ears), 4" wide, and 2" tall including the mating connectors. Not including the connectors, the case itself is 1" high.

Where is this product manufactured?

    • The ECU is manufactured in Suwanee, Georgia, USA. The wiring harness is also American-made.

What is the warranty on the MS3-Pro?

    • It carries a one year warranty against manufacturing defects.

How watertight is the box?

    • The case uses an o-ring seal and sealed connectors to ensure it is completely splashproof, and will keep water out if completely immersed up to a few inches for a few  minutes (which normally shouldn't happen, right?).  If you need further water submersion resistance that can be accomplished with a small bead of silicone just inside/outside of the o-ring.

Will I need to modify the harness to fit the mods on my engine?

    • This harness works with car, truck, and most aftermarket intakes that use a forward facing throttle body. Intakes that use a center mounted throttle body, independent throttle bodies, or reverse mounted intakes (with the throttle facing the bellhousing) will require minor modification.
    • The alternator connection is set up for an alternator mounted high on the driver's side, like the truck or Corvette accessory brackets. Setups that mount the alternator low (Camaro, Firebird, GTO, and CTS-V, for example, as well as many aftermarket setups) will need an extension. Our alternator extension harness provides a good way to add this.
    • We anticipate most customers won't be using the factory O2 sensors. We have brought these out to an Amphenol AT connector for making your own O2 harness.

What size screws do I need for the fuse box mounting?

  • It uses #10-32 mounting screws.

Does this harness have the MS3-Pro controlling the alternator?

  • No. You will need to wire the alternator to the charge lamp. That will activate the alternator. See details in the manual.

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