Chassis (Ground) Point
The physical point at which the negative return path is connected to the vehicle body on a negative ground vehicle. The connection must be made to unpainted, rust-free and solid metal; a serrated washer must be used. A bad ground creates a resistance that does not show up in measurement but appears under load, and produces false faults that hide the real cause.
The insidious side of ground resistance is this: in an unloaded measurement the multimeter may show a value close to zero, but with 10 A flowing the same connection creates a noticeable voltage loss. That is why a ground is always assessed under load.
- The correct test: with the system running, measure the voltage between the device's negative terminal and the negative post of the battery. A difference greater than a few hundred millivolts is a sign of a ground problem.
- Choosing the location: prefer the ground points left by the manufacturer rather than the engine block or painted sheet metal; failing that, scrape off the paint and connect to clean metal.
- Protection: after the connection is tightened, apply a thin protective grease or spray over it; a point left exposed will rust within one season.
A large proportion of the complaints coming from the field, "the motor sometimes works and sometimes does not", "the switch light flickers" and "the behaviour changes when the tractor is running", are ground related. Taking this measurement before removing the kit often ends the problem.
The context where this term is used: Converting a tractor hydraulic lever to electronic control