[krokodil]

My left front turn blinker started to fail randomly. It looks like there is some loose contact inside the assembly.
When I knock on it it starts working again.
My question is how do I open it? I tried to open it with a knife but I am afraid to break it.
There is a small hole with a rubber seal on the back but it does not look like a screw.

 

[STroadster]

Very likely not designed for disassembly because of the myth that LEDs can't fail. Unless your still under warranty the best bet is probably to get a cheap replacement set from Chinese Ebay.
21mm Clear Front Rear Plastic LED Turn Signal Indicator Amber Light For Triumph | eBay

 

[Jadorff]

no you can not open them when they fail you have to get another