Hillberg, the spare fuse that you describe is next to the warning light test switches under the cowl on the right hand side and that one is for the clutch. The 'relay' is actually part of the oil gauges system, the oil pressure sensor.
As Powerlimited says, the fuse pictured is a fuse to protect the by-pass wire that runs the clock and the RPM gauges. The RPM gauges only get power though when the clutch is engaged. The wire is referred to in the POH/RFM on page 7-12, Systems.
To know if the fuse is working or intact, check the clock prior to start. If it is not working, then the fuse is blown.