15 volts is too much it should be around 13.5 max at the battery, this should be pretty constant regardless of engine revs once above tickover.
If it's a 98 bike it won't have a Ducati decal on the tank.
My yellow cables were fried at the plug connector, do as suggested, although I just used inline crimps with no problems since.
If your battery reads less than 12.5 volts off the bike after a full charge it's probably knackered.
Just got a DETA 16AL-A2 battery, very good quality just over £35
ps. I don't know what i'm talking about.
[Edited on 29-1-2006 by sharpo]