Earthing

[John Wakefield]

On returning from the Cambridge Section Club Night on Thursday I noted on putting the East Coaster away that the speedo light was dimming slightly when I turned the handle bars. An investigation later confirmed an earthing fault. On checking with my good old fashioned AVO meter there was a 10 ohm resistance when connecting from the headlamp to the frame. ie the earth return for head, pilot & speedo bulbs was going via the steering head bearings, not a good idea as apart from poor lights it can also damage the steering head races. In my case I found that a bullet connector in the earth return under the seat was corroded & causing the resistance. A quick clean up of the connecting 'bullets' had the circuit resistance free & lights working brightly.
Most electrical problems on bikes are due to poor earthing & where possible wired earth returns should be made, do not rely on the frame to do this function. Equally the engine on the twins which have rubber bushed mountings also need a good wired earth return for the ignition coils. Again a poor earth here can result in poor starting or running of the engine.

[Brian Catt]

Good advice John. Earth (or Ground) circuits are vital to good electrical performance and should take into account the load that may be put through them. Bikes and Kit or modded performance cars are always suspect in this aspect. I was once asked to look over a modded Mini that had bad lights and found the earth return was only one thin cable, expected to carry the current for 2 headlights/sidelights, 2 spot lights and the intermittents like hooter and winkers. "It's earthed isn't it?! was the owners reply when I told him that was his problem.