Fundamentals of Electricity In Motorcycles

I learned the basics of electricity by buying and driving British motorcycles. In the 60s this was probably the quickest way to learn all the ins and outs of the topic. Either that or take up long distance hiking. In those days, most if not all motorcycles came with only one fuse, right next to the battery. If anything at all went wrong, it blew and the whole bike went dark.

There was a quick way to diagnose any electrical problem at all back then, since most of them involved a wire somewhere that had rubbed against something until the insulation was gone, and shorted out, blowing the fuse. The riders job was to find the rubbed spot and move it away from the ground spot at least long enough to get you home.  You did this by sitting on the ground next to your bike, where you could see most of the harness, remove the blown (15-20A) fuse, and prepare the 50 amp slo-blo. This done by wrapping the blown unit in some foil from your cigarette pack. Yeah, everyone smoked.

Place the new fuse in the holder, and push it together with the key on, and watch the bike carefully to see which wire began smoking. Voila! you found the culprit. Move the afflicted wire away from whatever had damaged it, perform the smoke test one more time to be sure you got the problem, then start up and motor on down the road.

The Japanese changed all this by copying the wiring from computer assisted cars into their motorcycles. Now you have to figure out where they hid the fuse box, pull all the fuses out until you find the bad one, figure out which of several components on that circuit was misbehaving, and figure out how to get the bike to run at all long enough to get you home. Not easy without a set of tools and a multimeter.

When my Little Red Bike suddenly quit the other day, it wasn't hard to figure out that the fuel pump had quit, so the issue was either a blown fuse or a blown pump. Since the fuses were all behind a panel held in place with 2 5mm socket head screws and I had no 5mm Allen wrench, which it was didn't matter, I needed a trailer. I arraigned for that, got the bike home where when I turned the key, the pump hummed merrily and the motor fired right up. I hate intermittent problems. They know when they're close to a tool set, and disappear.

Previous owner had replaced the stock fuel pump with an aftermarket one from Auto Zone. Nothing wrong with that, but the wiring was not plug and play so he added about 6" of extra wire and a couple of quick disconnects. Here's your lesson for the day: QDs work OK under normal circumstances, but motorcycles are not normal. Under high vibration, they can become slow disconnects, the sort of thing Joseph Lucas probably invented. Mr Lucas is also known for having invented the intermittent windscreen wiper. Also the intermittent headlight and ignition system. The QDs are now gone, the wires are soldered, and the bike seems to run fine.