Here's how the switch works:
It actually close FOUR circuits individually;
(note - the wire colours listed are the ones on the main harness side - you will need to match these up to the switch which uses a different colour set!!)
1. White/Blue from Fuse #2 - constant Power In -> switches to Green (Ignition Circuit) which goes directly to the Kill/Run Switch
2. White/Blue from Fuse #2 - constant Power In -> switches to Blue/Yellow - Lighting Control - goes via Fuse #8
3. Orange from Fuse #4 - constant Power In -> switches to Orange - Stop/Turns/Horn goes directly to the Front & Rear Brake Switches and Horn Positive
4. Red/Blue from Fuse #8 (output from the fuse supplied by the Blue/Yellow) -> switches to Red/Orange - Running Lights - goes via Fuse #10
Some general Diagnostics:
ALL Fuses except 8, 9, 10 (9 is actually empty) should have 12V on them EVEN WITH KEY OFF.
With Key ON you should have power at Fuses 8 and 10
To measure voltage at Fuses, use this technique:
Put the voltmeter negative probe on battery negative and leave it there;
Next take the red probe and, leaving the fuses installed, simply touch the probe to the metal tabs on the tops of the Fuses.
There should be 12V on EACH side of the fuse as appropriate
For the Ignition Circuit, it does not go back through a Fuse - the easiest place to measure the voltage for that circuit (the Green out of the Key-Switch to the Kill/Run switch)
would be at the Alarm Connector under the tank;
There are two wire loops on that blanking connector - the loops are between pins 1 & 2 and pins 3 & 5.
With Key On you should have 12V on all four of those pins - you might find it easier to use a needle to touch the terminal as the probe will probably be a bit too large to make contact. (I would just pick one to check - if one is good they will all be)
The other way to go is just to disconnect the switch and measure for continuity:
With the connector held in this orientation, with those ribs towards the top;
looking directly into the terminals (NOT the wire side)
Top Row Left to Right is 4 - 3 - 2 - 1
Bottom Row Left to Right is 8 - 7 - 6 - 5
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With switch ON, you should have continuity between
1 & 5;
1 & 4;
2 & 3;
6 & 8.
Hope that helps
Let me know if you need further guidance