Yamaha Service Manual depicts the block being the ground point. For multiple components. One of which is the TPS. I can envision an intermittent ground causing all sorts of mayhem.
One option would be to get two individual switch plate panels and transfer your components from the old single switch plate panel to the individual switch plate panels. Then mount the new switch plate panels side by side. Kill switch on what ever side is preferred.
A short section of tubing runs from the lower unit to inside the cowling. From there the short section of tubing connects to a longer section that runs from the motor to the boat and on up to the speedometer.
You either have voltage to the fuse or you don't.
You either have voltage across the fuse or you don't.
As seen in the diagram, the fuse powers both of the trim switches and the starter motor relay.
