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Replacing My Yanmar 2GM20 Wiring Harness

In this video I attempt to resolve a nagging issue with my Yanmar 2GM20 Marine Diesel engine, specifically it not always starting reliably. Having exhausted the obvious things like dirty fuel filters and air in the fuel line, I turned my attention to the electrical portion of the engine.

Finding that cleaning connections in the wiring harness seemed to resolve the problem at times, I opted to replace the wiring harness altogether. The harness, compatible with a number of Yanmar Marine Diesel models including 1GM, 2GM, 3GM (F)(D), 2GM20 (only on engines before serial # E21167) and 3GM30 (only on engines before serial # E14020)) has the manufacturer’s part number of 370-128270-77921, an updated part number from the original. It’s available in a number of places, including at the following:




I do recommend shopping around, as prices for this part vary greatly!

Installation is relatively simple, with all connection points located on the port side of the engine. My approach was to begin at the back and work forward, disconnecting the old harness and connecting the corresponding wires of the new harness.

Here are the steps I followed to change the wiring harness:

  1. I started with the connectors leading to the engine control panel. (5:48)
  2. I followed that with the ground and harness clamp at the engine mount. (6:46)
  3. After that, I connected the tachometer sender (8:56) before moving forward on the engine.
  4. I connected the starter motor next. (9:54)
  5. Followed by the alternator and voltage sender/charge lamp. (14:29)
  6. Lastly, I connected the temperature and pressure sensors. (16:47)

After completing these steps, my 28 year old Yanmar started up on the very first try, and I’ve not had any issues starting her since!

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