Apologies to all those who already know this but as I'm generally scared of anything electrical I thought I'd share some experience.
Short Version
If you've fitted LED globes and they won't work, try reversing the wiring connectors.
Long Version
I actually quite like the look of the OEM indicator stalks and have no problem with them being both visible and sitting out out the way they do. I swapped out the lenses a year or so ago with clear ones and hated the look on my bike so I swapped them for the dark smoked ones, which I reckon look great. Only drawback is the visibility of them. I was being told they're just not bright enough so I got myself some LED bulbs to put in and a replacement flasher unit.
Simple job I thought. I put the bulbs in, replaced the flasher and gave it a whirl. Only one globe lit up and there was no flash. WTF.
Then I put the original flasher back in because I'd heard you'll still get a flash, just really fast. Nothing.
Not sure why, and just as I was about to put the old stuff back in, but I remembered that, unlike ordinary bulbs, LEDs are sensitive to the way they are wired up. So I pulled the three non-working indicators apart and reversed the connectors on the pins inside. Bingo. Ish. Ish because I now had 4 indicators lighting up but still no flash.
I had another go with the old flasher unit back in and hey presto, flashers, albeit really fast and loud clicking. Faulty flasher unit I thought. Apparently so! New flasher unit fixed it and I'm real happy with the result!