Earthing the gearbox to the body

Hello, you stress the importance of having only one connection between the engine block and the body. But I also heard it was important to also connect the gearbox to the body as well. What’s you insight on this ? Thank you

This would seem to be a good idea, but there is a phenomena called "ground loops", where the actual relative voltages of a 'ground', or 'earth', can vary depending on the location and the amperage of currents through the earth - remember, in order to get a current to flow it has to be pulled/pushed by a voltage difference, even in something that one might assume to be the same throughout.

This is why it is important to use a single point for an earth for most electronic circuits, as they will typically operate in differences of milli' or even micro' volts or amps - that's thousandths or millionths, so you can see how even a litlle difference is important!

When you introduce a second engine/chassis earth point you can not only affect the ground potentials across the engine-transmission, which can affect their electronics, but also between the chassis points that they're grounded through.