diode

is there a test or how can one tell if a diode in the harness under the tach has gone bad?

3H5-81980-00-00 #14 in this schematic http://www.partzilla.com/parts/search/Yamaha/Motorcycle/2001/V-MAX+-+VMX1200N/ELECTRICAL+2/parts.html

OK sorry for the double post but I'm desperate here.. I found this in my harness: I do believe that it is actually a diode - it was plugged in between a blue/white (L/W) and a green (G) wire, in a clear sleeve just under the TCI unit. The only L/W wires I can find in the wiring diagram lead...

Last weekend I rode 350 miles to Elko, NV for a rally. It rained like crazy the first night and of course I didn't have a cover. The next morning the bike was obviously really wet. We rode downtown to the rally, and I parked it. The weather got better and it turned into a pretty nice day...