Id be willing to bet that you will lose some useable lighting unless viewed from directly behind with an LED 1156. I know there are some newer designs coming out (Phillips) that may have better viewing angles. Not much light back there on a SG. I wouldn't waste my money on a cheap 1156 replacement. It may look great from directly behind but noticeably dimmer viewed from the side.
Like Joker said...I tried them in my trailer and they weren't very bright and I could only see them directly behind the trailer. Custom Dynamics is the way to go....
I had run Led 1157 towers with success in other bikes but the sockets on they Harley bullet signals are just too deep in the reflector for most tower LEDs. I've bought a few brands over the years and none fit. Custom dynamics is definitely the way to go.
I've gone the cheap(er) route many times, thinking I'm saving money...only to find out later it would have been better to spend the extra money initially. Think about this....they are very bright (cars can see you better), probably never have to replace them again and because others can see you better, will save you from having to spend your deductible (and time not riding your scoot...) when someone crashes into you because they couldn't see you....