The wiring in the Diablo 503 is different than that of the 500 & 502 in that the 503 has electric start and a charging system. With that, the wiring is a little more complex.
First off, lets talk about the key switch. In December of 2009, Steve from Toronto, Ontario shared this story:
Hi Bruce: To all that have a 503 beware. My ignition switch shorted out sending 12 volts down into the points starting a small wiring fire. After my frustration level came down I began to research the problem. Inside the key switch the brass disc had fallen to one side and this was the cause. The solution was a new ignition switch (that is not available anywhere around me). I also had to replace the coil and stator. I got a switch for a cub cadet tractor but had to put in a toggle switch as well. The ignition switch now turns on my lights and cranks the engine and the toggle switch turn on the ignition. My 503 is now running perfect
I hope that this info will prevent others from going though what I did. So if your key switch feels sloppy, change it and avoid my grief.
The good new is Key Switches that match the original functions of the original switch are now available. In addition, connection plug with a harness attached for the back of the switch are also available which protect the “hot” positive connections from shorting out when you are swinging a wrench in the area trying to get the spark plug out. Sparks above the gas tank are not great at any time.
