Genuine Woodward Electronic Speed Control Actuator to upgrade an engine with a mechanical governor to electronic.

Woodward Part # 8404-5003

Function: The 8404-5003 controls engine speed by integrating an electric actuator with speed control software.
Compatibility: It's compatible with Stanadyne DB4 fuel pumps and can be used as a replacement for the ST-125 speed control.
Integration: The actuator combines the electric actuator and speed control software into a single, integrated package.
Voltage: The actuator typically operates within a voltage range of 10-32VDC.
Temperature Range: It's designed to function within a temperature range of -40°C to 105°C.
Applications: The 8404-5003 is used in various diesel engines, particularly those with Stanadyne DB4 fuel pumps.

To upgrade an engine with a mechanical governor to electronic with a Stanadyne DB4 fuel pumps you will need Woodward P/N 8404-5003 or 8404-5007 depending the location of the pump on the engine.
Diesel engines typically equiped with Stanadyne DB4 are Cummins G-Drive series 4B, 6B, John Deere 3029,  etc 

The Woodward 8404-5003 is an electronic speed control actuator, often used to replace the ST-125 speed control.
It's designed to be a functional replacement and includes new features not found in the ST-125.
This actuator is typically used with Stanadyne DB4 fuel pumps, especially on diesel engines like Cummins G-Drive series 4B, 6B, and John Deere 3029.

See Woodward Application Note 51285 (Revision A) Original Instructions titled:
Replacing the ST-125™ Engine Control with an L-Series Speed Controller 8404-5003

Woodward’s L-Series Speed Controller can be used as a functional replacement for the ST-125™ Speed Control. The L-Series 8404-5003 speed control was designed with many new features and functions that are not built into the ST-125. The Woodward L-Series combines the L-Series electric actuator with integrated speed control software to control the speed of a diesel engine. The L-Series utilizes a microprocessor-based control that is incorporated into the actuator, creating a single, integrated package. This eliminates the need for an additional driver box and speed control box. Refer to Woodward manual 26250 for details on the L-Series additional features, operation, adjustment, and troubleshooting.