How is the cable extended when the distance between the cab and the engine is long?
The GS740-3P comes with a ready-made 2 metre IP67 connectorised harness per channel. Over longer distances the supply cable is extended by increasing the conductor cross-section, and the potentiometer cable preferably by using shielded cable. The shield is connected to the green wire, that is, to the potentiometer GND. Joints must be soldered and insulated; temporary terminal-block joints must not be left in place under engine vibration.
In an extension, two lines are subject to different rules.
1) Supply line (red/black). As length increases, voltage drop increases. When the servo draws current at start-up, a thin cable causes supply fluctuation. The solution is to increase the cross-section; also place the line's fuse close to the battery side.
2) Potentiometer line (green/yellow). This is a high-impedance analogue signal and it is sensitive to noise. Over long distances:
- Use shielded cable and connect the shield to the green wire at one end only.
- Do not run the signal through the same channel as the supply, starter and ignition harness.
- Take the GND reference from the system's own green wire, not from intermediate points; a reference routed through the chassis produces drift in speed.
Making a joint: solder the ends and insulate them with heat-shrink tubing. A screw terminal loosens over time under engine vibration and leads to interruptions that are hard to diagnose. Removing the IP67 connectors and making an open joint in their place also destroys the harness's protection rating; if possible, extend upstream of the original connectorised harness without disturbing it.
After extending, turn the potentiometer from end to end and verify that the response is immediate and free of jitter.
Full topic: Electronic speed and throttle control on a diesel engine