Tom, that sux...
To state the obvious, you have a short somewhere. FIRST, do step one: Look for a pinched wire, by tracing the circuit from the fuse board up through the bike. It is hopefully a simple pinch or worn through insulation and a visible short you can find.... I give this a high likelyhood... If not then you have to try and isolate it to one of the components involted by the method of one by one hookup until the fuse blows. In the course of both of these, I would give it a 95% chance of finding it. Use good lights, trace it out carefully, look closely..
If you are handy, step two is more involved and you are going to have to do what the HD Shop would do and I think you need to pull the fairing off. Look at all the gauges involved on the that power leg and try to find something vibrated through, worn insulation, pinched wire, something that would cause this short. You might get lucky and find a visible fault, look closely, as the next step would be more involved again...
Failing that, the short could be internal, and this takes a step by step total isolation and hook up one by one. What I mean is you need to isolate this power leg causing the problem, off of all the gauges involved at first.. Tape up the ends, and if the fuse does not blow with the bike idling then shut it off and hook them up one by one, starting the bike each time. You do this to see if you have isolated it or that gauge is ok, then turn off the bike and hook up the next one... The last hookup before the fuse blows will isolate it down to that one defective part if the short is internal and not visible. This is a time consuming way to attack it, but you are saving the big Shop time costs. In the course of this, you are likely to find the short.
Good Luck, Cowboy in Australia