Short to Chassis
The insulation of the positive line being damaged and touching the vehicle body. In a negative-chassis system this means a direct short circuit. Because it forms when a cable passes over a sheet-metal edge or rubs against a moving part, it generally appears with vibration and over time.
A fault in full contact blows the fuse; in partial contact it behaves more insidiously. A high-resistance short shows up as battery drain, a hot spot, or operation cutting out at a particular angle of movement.
- Diagnosis: switch off the power, disconnect the line concerned and measure between the conductor and the chassis with an ohmmeter. On a sound line the reading should be very high or open circuit.
- Intermittent short: move the cable by hand along its route while measuring; a jump in resistance narrows down the contact point.
- Common locations: sheet-metal hole crossings, under clamps, door and bonnet hinge areas, points touching hydraulic hose.
- Prevention: using a grommet at every sheet-metal crossing, fixing the cable at 15–20 cm intervals, leaving free slack at moving parts.
In the repair, rather than wrapping the damaged section with sleeving and moving on, the route must be corrected and protection added, because the same chafing will otherwise recur.
Context in which this term is used: Installation, redundancy and field continuity