I did return the GS100 and bought 2 1157 strobe bulbs for the brake, they work fine.
I replace the rear 1157 turn bulbs with LED, but they do not work.
I'm planning to replace the 2 front turn bulbs (1156) with LED.
Do I need to replace the relay to make them work properly?
Remember this is a VT1100C- 2007
As for the rears turns not working are they actually 1157's or 1156's? (I know these are incandescent pictures but they are there for the base connection reference)
Even with a stock flasher unit that wasn't made for LED's the bulbs would flash, just at a faster rate (like when an incandescent bulb would burn out.)
So, yes you'd need an adjustable flasher for LED's to get the proper flash rate.
This doesn't explain though why the rears are not working.
Do they work with good incandescent bulbs? (to rule out bad switch, wire, fuse etc.)
Can you provide a photo of the base of the LED bulbs you have and one of the inside of the socket the bulb goes into?
I have seen bikes that use the 1157 socket but only used half the bulb's filament.
I'm surmising either the polarity of the wires is incorrect (thus the bulb won't light) OR the bulb is in wrong OR the bulb makes connection with one of the pins in the socket that has no power.
Easiest thing to try is to turn the bulb around to see if that fixes it. If it does the bulb was just in wrong.
You can check the power in the socket with a multimeter. Set it to 12v dc or higher and with the flasher activated and the bike ignition "on" put the ends of the multimeter into the plug.
You want the negative (black) wire on the outside of the socket and the positive (red) to touch one of the pins on the bottom. If it's a digital meter you want to see +12v (ish). That means power is on the bottom pin and ground is the outside. If it says -12v it means the power is on the outside and ground is the center, which is highly unlikely, or you have the red and black leads swapped on the meter end. If it's an analogue meter you want to see the needle swing towards 12v and not in reverse.