Tractor Repair: Auxiliary lights, new tractors, voltage variations

Question
I am hooking up some lights, and I was wondering why I would need to hook up the ground to a ground on the chassis, instead of hooking it up directly to the (-) side of the battery? It seems that it would be a better circuit, but who knows? I read somewhere a long time ago that you shouldn't do that, but don't recall seeing a reason why. Thanks for any input!

Answer
Hello,

  You could ground everything on the tractor to the battery if you wanted to, but it would be pointless and use lots and lots of wire.  The battery cable on the - terminal of the battery is grounded directly to the chassis, so any lights or other electrical equipment only need to be grounded to the chassis in order to complete the circuit and function properly.  New tractors that have lots of computers on them have what is called "clean grounds" meaning the computers are grounded directly to the battery because the electronics are sensitive to voltage variations.  For lights, a chassis ground is all that you need and will save you lots of wire.