Where should I take the chassis (earth) connection of the lift retrofit kit from?
The negative supply must be connected with a serrated washer to a point cleaned of paint and rust down to bare metal that is genuinely electrically bonded to the vehicle chassis. The cross section must be the same as the positive wire; use at least 2.5 mm² for a 10A load. While the kit is running, the voltage difference between the kit's negative terminal and the battery negative terminal must not exceed the 0.2 V target derived from the 3% voltage drop allowance.
To choose a good chassis point:
- Make sure it is real chassis. Panels mounted on rubber blocks, plastic parts and painted bodywork sheet surfaces do not give a reliable return path.
- Prepare the surface. Sand off paint, rust and coating; after making the connection apply a suitable protective to prevent corrosion.
- Fastener. Use a serrated washer and a bolt tightened to the proper torque; prefer a locking nut against loosening under vibration.
- Keep the distance short. The closer the chassis point is to the kit, the lower the resistance.
- Do not share a common point. Avoid sharing the same bolt with high-current consumers such as the starter motor.
One of the most common complaints, the motor turning slowly or weakly, is most often not a kit fault but a poor chassis connection. This voltage difference is the first value to measure in diagnosis. Alternatively, a separate negative wire run directly to the battery negative terminal can also be used.
Full topic: Converting a tractor hydraulic lever to electronic control