yamaha tach for F100

[scallawah]

my boat is rigged with twin F100s,however the tachs does not light at all.Trim and hour meter works find.I need to know what's the purpose of the set and mode button as well.

assiatance is greatly apperciated

[boats.net]

The blue wire may not be connected in back of gauges. The harness that goes between the gauges and key switch has an short Yellow and Blue wire,connect them togather and the gauge light will light up when key is turned on. The mode button toggles between the different function's of gauges and the set button resets the trip meter on gauges.