A positive ground system works by directly connecting the chassis of a vehicle to the positive side of the vehicle's battery. This system effectively earths the vehicle as the chassis attaches to the battery using a positive battery cable. The cable is tethered to the battery at one end and the engine block at the other.
The positive ground method was common before the year 1954, and many vintage or classic cars, especially those from the United Kingdom, adopted the positive grounding system. Most modern vehicles use a negative ground system that involves wiring the vehicle chassis to the negative side of the battery, and this has many advantages over positive ground systems.
Negative ground systems allow the driver to plug electrical devices into their vehicles, and this is especially useful for modern commuters that make use of devices like GPS systems or wish to charge a smartphone using a cigarette lighter of USB attachment.
The evolution of the less functional positive ground system is easily explained, as before the invention of PVC-insulated plastic wiring in the 1960s, live wires were covered with cloth insulation that performed poorly in the damp conditions found in the U.K. and other European nations.
Damp insulation would often corrode, but positively grounded wires are noticeably more resilient to the elements, which led to the propensity of positive ground system wiring in older vehicles.