Wiring improvementsUse separate earth cables for better electrical connectivity.
An electrical circuit must be continuous from one battery terminal to the other.
Many early machines did not have good earthing (grounding) of electrical circuits and relied on a good connection where an appliance screwed to a frame. Headlights are earthed to the frame via the headlight brackets and the steering head bearings. Tail lights are connected to the number plate bracket, to the mudguard, to the mudguard stays, to the frame. Engines often rely on mounting bolts in painted engine plates.
To improve the electrical circuit and make lights brighter and engines run smoother run separate earth wires from the battery earthing point to inside the taillight, inside the headlight shell and to the motor. Earth wires must be as heavy as main power wires / cables.
Inside the headlight shell, the following earth points can all be connected to the main earth wire: headlight bulb holder; headlight pilot bulb holder; headlight shell; main power switch if required. Also branch off to the handlebars.
LED bulbs require a perfect earth. If there is too great a resistance on the earth (return) side of the circuit the LED light will not work. An incandescent bulb can glow if it can earth itself through another circuit.
Ignition lead resistance and spark plug resistance is critical for good performance of magneto and early coil ignition. Test your ignition leads from the end that goes into the magneto to the end that connects to the spark plug. The resistance should be zero or only a few Ohms. If the resistance is higher check the HT lead and the plug cap separately. If either has a higher resistance replace it with an item with zero resistance. Repeat the test with the spark plug, measuring the resistance from the top where the plug cap attaches to the centre electrode where the spark fires across the the plug body. Again if the resistance is more than a few Ohms replace the plug. With spark plugs 1000 Ohms makes a big difference and several thousand Ohms may make a good idle and easy starting hard to achieve.