(IMO, of course. And Geek Alert)
This is the switch and tuner schematic for an MFJ-949E Versa Tuner II. Great little unit, with a built-in dummy load. It has a switch that selects the dummy load, then the three antenna connectors in pass-through mode, then the three antenna connectors through the matching network, and then the dummy load again… through the matching network.
Which means that if you want to tune into the dummy load, you have to use the setting all the way to the left, or you have to adjust the tuner to match the dummy load to the rig, using the switch setting on the right.
Now why would you need to match a 50 ohm dummy load to your rig? Insane. The dummy load switch setting on the right should connect straight to the dummy load, not via the tuner.
I have a soldering iron, I can fix it.