I just ordered a pair of bulbs (only trying the rears for now) and a flasher relay from Better Car Lighting. The bulbs are good, appreciably brighter. However, when I try to swap in the relay they supplied, it blew the fuse. Same outcome either for indicators or hazard lights (I didn't repeat too often, to avoid running out of spare fuses!). Put the old relay back in and it works fine (with old bulbs or LED, albeit flashing too fast with the LED bulbs), so it's definitely the supplied relay that's the problem.
According to Gil at Better Car Lighting, some cars use a Bosch relay where one of the pins goes to earth, which is different to the relay used on other cars. If that is the issue, he has a different relay that will work with that system.
Has anyone been down this road already and know the answer? If not, I'll start digging in to wiring diagrams and try and work it out...
These are pics from the website, what turned up doesn't look identical but it's probably just cosmetic.
The new flasher relay:

And the bulb:

 
							

