I had a HISS hiccup after the winter service, v similar actions from the light - sometimes full brightness, sometimes dull & flickering.....
I stripped/lubed the kill switch starter button & slight improvement then wiggled the connector for the HISS pickup (r/h/s of clocks i think) it's the one with waterproof connector & that sorted it, so lubed it & i think i tightened the female connectors (gently with pliers).
Been fine since
Blooming troublesome bike - last time was the headlight bulb went.
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'02 - 650 Transalp
'92 - VFR750
'91 - NC30 (UK spec)
'08 - 600 Hornet for sale (kind of....)