Your problem is that you don't have enough power running through your bike at no revs (charge your battery and you'll be fine!).
Your relay is fine - it works perfectly on the left hand side, yes?
Check for a short between your r/h indicator circuit and your headlamp power feed. I suspect the short will be in the grounding half of the right indicator system, between that and the + feed for the headlamp (or possibly between the + feed to the indicators and your - feed from your headlamp).
It's gonna be a short somewhere... So do the following:
1) Understand your indicator and headlamp circuits (that means go read the wiring diagram and memorise those circuits... IIRC the brown and dark green wires run from your switch gear to the left and right sides of the indicators, the light green and yellow wires power your dipped and full beam, and most of the grounds are black!!!).
2) Go buy yourself a DECENT multimeter (should cost about 20 quid or so) with a continuity tester (a beeping one is preferable, trust me) (that goes for EVERY SINGLE MEMBER of this forum who thinks they'll ever do any work on electrics, in other words, most of you!).
3) Trace through your indicator system running continuity tests throughout the whole lot.
4) Test EVERY SINGLE PIN on the switchgear multi-block for shorts (the switches are actually shown VERY well in the wiring diagrams, and it's fairly easy to understand what connectors should be linked in each state for the switch gear).
5) Apply a little luck, and a VERY VERY large amount of logic to the situation. It's gonna be a problem between your right hand indicator circuits and your headlamp circuit.
6) Ask yourself questions such as:
What if I have my main beam on rather than my dipped beam?
What happens if I have my brake lights on at the same time?
Will this affect my horn as well?
Did I b*st*rdise any connectors last time I was working on anything?
Did I accidentally nick any wires, or feel like I broke any?
Does it do it when I only have my parking lights on?
7) If all else fails, give me a shout (my mobile number's coming your way in a PM).