The three wires are, running light hot, blinker hot and ground. The green one is ground the other (orange or light blue, with or without a stripe) are your hots. Make sure one of the ones you have hooked up is the green ground, and that it goes to the negative on the led assembly as led's are directional and they won't work with the polarities reversed. Then hook the positive wire on the led to the blinker hot, it should only go hot when the blinkers flashing. Voila, done. If the above doesn't work then you either have the ground hooked up backwards on the led assembly, you blew a fuse or you fried the circuit wires entirely from hooking them up wrong (unlikely).

As for what woot commented on above, th circuit he was refering to uses diodes, not resistors, to duplicate the effect of 3 wire lights with running lights that stay on when the blinkers not active and it doesn't produce any additional heat. When resistors get used is when you go the cheap-o method of slowing the blink rate of led's by putting parallel resistors along the led's to draw more current through the blinker circuit and slow the blinkage, and yeah, that generates a lot of heat. It's far better to replace the stock flasher unit instead with an electronic one that self regulates it's own speed without relying on a current draw.

And yes, this has been discussed to death and theres a how-to in the how-to section. Doesn't mean your particfular situation might not merit some attention though. Every problem has the potential to be different from the other 100 times it's been brought up on the site. No worries.