OK, I am going to give you the “Long Story”. Yes there are shortcuts, but I want you to see the big picture and understand how it works.
To do anything, electricity must flow in a circuit, from the source (battery + ) and back to the source (battery – ). So, I am posting a wiring diagram for you to follow. Your voltage indicating light is good enough for this operation. Start off by connecting it to the battery (-) terminal and leave it there for the duration of the test. Use an extension wire if necessary.
1. Notice from the diagram, a heavy cable runs between the battery and one side of the solenoid. So touch your light to that side of the solenoid,, and it lights up, right? That tells you that electricity gets that far, and now we are going to follow it the rest of the way through the circuit.
2. There is a green wire from where you are, leading to the “B” post on the key switch. Touch your light to that “B” post. Should light up.
3. When you turn the key to “Start”, electricity is directed to the “S” terminal on the switch. Touch your light there and turn key to start. Should light up.
4. Now, a white wire leaves the “S” terminal and back to one of the small posts on the solenoid. Touch your light there and turn the key to start. Should light up
5. Electricity flows through a coil inside the solenoid and out the other small post. Touch your light there and it should NOT light up. Why? Because that post is grounded through the mercury switch. BUT if it DOES light up, the mercury switch is not grounding it. Reason might be a broken wire, or throttle position set too far toward fast, or mercury switch case not grounded.
6. Last test, touch your light to an unpainted spot on the powerhead and turn the key to start. Should NOT light up. Again, because it is grounded through the negative battery cable. If it does light up, there is a problem with the engine ground.
7. Throughout this, I have ignored the cable plug on the side of the motor. If any tests fail, suspect a problem wit that plug.
