Can someone describe the method for testing the M2 'Switch Box" component?

[Palm Bay Chuck]

I suspect that I have a bad switch box which is causing my engine output to falter when it hits about 4,000 RPM. The 210 HP M2 engine has 2 of these switch boxes. As I understand it, one switch box handles 3 cylinders on one side of the engine and the other switch box handles the other 3.

I purchased a new one, but I'm not sure which of the two installed could be the unit that is failing and I'm wondering, is there a way to test them OFF the engine with a multi-meter? Or is it easier to test them ON the engine?

I've seen some hints about checking cylinder temp after running the engine for a bit to see if one if 1 side of the engine is cool, but to do this test, I'm thinking I'd have to run at high RPM's and right now I'm not near the water.

Any advice on how to test is appreciated. I've been putting off this project fearing that it's beyond me and I bet it's going to be a simple project! Thank you.

 

[Sportster-2001-951C-Stock]

Also consider the electronic idle compensator perhaps, if your has one. I understand they also can become flaky. As far as troubleshooting this on trailer goes, I doubt you can, really.

Swapping the new box for the old box is how I'd do it, probably. That means you might be forced to swap that box a couple times.

I'm not sure about being able to isolate which cylinder is misfiring necessarily unless it's consistent the heat will no build so touching the plug shell can reveal a cylinder that's not making power but I usually go right to pulling a plug wire while the engine is malfunctioning. If pulling a plug wire completely off the plug results in no change, that's the cylinder which isn't firing.

If by holding the wire 1/4" or so away from the plug top the cylinder begins firing, this confirms the plug is fouled. Forcing the spark to jump from the wire to the plug allows the coil voltage to build, this sudden discharge once the voltage builds is often enough to jump the gap of a mildly fouled plug.

You can also sometimes locate an ignition miss by using an inductive timing light, just realize a timing light flash doesn't necessarily mean there's a spark jumping the plug gap. More like, this method tells you there's no fire whatsoever in the coil. The reason is, inductive timing lights are pretty good at reliably picking up even a weak signal that otherwise too weak to fire a plug.

IMO

 

[Palm Bay Chuck]

Well, I figured I'll swap the INNER box while on the trailer. That's the harder one to get to. Then take it to the river and give it a test. And if that doesn't help, I can swap the outer one while sitting in the water.

Thank you for your advice!