Custom Standalone ECM / TCM harnesses (LB7, LLY, LBZ, LMM)

$586.00$1,800.00 has worked to develop the cleanest solution for wiring your Duramax drivetrain for simple operation with nothing more than power, ground, ignition and cranking signals. This harness is the connection between the ECM/TCM and the engine harness as well as the transmission.

* This harness requires ECM tuning and we recommend TCM tuning as well (see the explanation in our article, Duramax Swap Custom Tuning).
** The “no donor” options are based on what we have in stock. Contact us for pricing on a new donor if you don’t see what you’re after in the list.

More information below.



Important info about our harnesses…

Lead time on harness conversion is generally 3-4 weeks from the time it is received and checked in. At the time of check-in, the harness will be inspected and subject to additional charges (either mandatory or suggested) if there are any issues with wires, corrosion, pins or connectors.

We do not support Duramax integration into late model vehicles. This includes any integration with any factory gauges, factory body harnesses, etc. It doesn’t mean it can’t be done, just that we don’t support it. You will not retain control of the AC, tow haul or any other factory features that are controlled through the BCM.

Your harness is set up for standalone use only which in basic terms means the engine will run and the transmission will function. Due to the complexity of modern vehicles and their control systems, donor vehicle functions, conveniences or “nice to haves” are not offered or supported in any way as follows:

Tow-Haul Mode, Tap Shift, Electric Transfer Case Shifting, Axle Engagement, Duramax Idle Up, Fled Fuel, Starter Solenoid Control, Park-Neutral Starter Interrupt, Shift Interlock, AC Compressor Clutch Control, AC Req Idle-Up, AC Req Fan Control, Cruise Control, Vehicle Lighting, Donor Vehicle Gauge Clusters or any other donor vehicle features/conveniences.

You will be responsible for wiring your owner starter circuit with neutral safety and your own AC circuit if you are wanting AC. You can still leverage any of the factory AC components you’d like but it will be controlled separate from the harness. We recommend aftermarket HVAC, controls and dryer at least.

Gauges: We offer a 10% discount on any available Dakota Digital products with the purchase of our harness (contact us with specific product requests). The harness will retain the OBD port, so you can use that for your gauges or use some of the harness pigtails and add an oil pressure and coolant temp sensor to wire them directly. We recommend the latter if you’re planning to use the OBD continually for anything else because the signal isn’t always strong enough on an OBD splitter to run two devices. The CTS3 monitor can be used as a gauge cluster as well.

If you are interested in our standalone harness you can follow our ordering guide, purchase your harness modification a well as the ECM and TCM tunes and we can certainly get it running and driving properly for you.


Any attempts to make the above mentioned systems or features function are completely up to the customer and/or the installer.

Modifications will void any warranty or support, so it is crucial that you test start your setup with the harness prior to making any modifications. If you have not made modifications to the standalone harness, have proper tuning and are having issues with your test start, please see our diagnostics form.

The harness can be configured to include following Inputs and outputs:


  • Cruise Control
  • 2wd/4wd operation


  • Speedo signal
  • Tachometer
  • Fuel pump relay
  • AC clutch command

The Harness includes a high quality fuse block for power distribution to the proper Ignition switched inputs (I.E. ECM, TCM, Fuel pump, injectors, etc.). A High current relay is also included to carry the current load for these circuits.

A communication pigtail is included in 4WD harnesses to interface with our standalone T-case controller for electric shift 263xHD transfer cases.

*This does not include the “engine harness” which should be purchased with your engine.

Convert customer supplied Duramax engine and transmission harness for standalone use as follows:

  • Remove all factory convoluted (loom) tubing and tape. Completely clean and degrease harness.
  • Retain Allison TCM or setup for 4L80E, 4L85E, TH400, Powerglide, or Manual Transmission. (customer choice)
  • Reconfigure harness for individual connector runs and a centralized ground.
  • Install a single fuse block and provide a main ignition power relay.
  • Install 12v Constant Fuse Link.
  • Install OBD2/ALDL Connector – 6 Feet Long. (longer available on request up to 55 feet for dyno use)
  • Identify Park Neutral Position connections and provide schematic for starter.
  • Identify Back Up Lamp connection on PNP switch and provide schematic.
  • Retain Duramax Alternator controlled by PCM.
  • Retain or Remove Glow Plugs and EGR circuits.
  • Identify Cruise Control pigtail connections at PCM and provide schematic. (LB7, LLY and LBZ only)
  • Remove all Air Conditioning control related circuits. Return to customer. (can be left in)
  • Remove Coolant Level indicator control circuit. Return to customer.
  • Identify Wait to Start, TCC and MIL lamp pigtail connections at PCM.
  • Identify Tach and Speedometer pigtail connections at the PCM. (LB7, LLY & LBZ only.)
  • Identify HiRes VSS pigtail connection at PCM. (Note: ABS integration is not recommended.)
  • Every harness is completely opened and electrically tested. No shortcuts!
  • 14 Day Turnaround on all harness work
  • Simple 4 wire hook up to make the engine run. (A Single Ground, 12V Constant, 12V Key On, Fuel Pump)
  • 6 Gang Fuse Block and OBD Diagnostic Connector included.

* Can be recovered with new High Temp Loom and High Temp Harness Tape.

Additional information

Weight 10 lbs
Dimensions 24 × 12 × 6 in
Model Year

2001-2004 LB7, 2004.5-2005 LLY, 2006-2007 LBZ, 2007.5-2010 LMM

Harness Type

Truck Donor, Van/Topkick Donor, No donor


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