I had this exact problem when I switched to 100% led bulbs on my max, the fix is simple but requires you to get elbow deep in your max. Ignore using resistors, they don't always work and they cause your leds to be way dimmer than they should be.
First, get an LED Flasher relay and install it on the brown and brown/white wires under your left scoop (just cut the wires off the factory relay and leave the rest intact, you can mount the relay with one of the factory screws in there).
Before you button that back up you'll need some rectifier diodes and some heat shrink tubing, also some solder and a soldering iron OR some crimp connectors if you aren't handy with a soldering iron because the next part involves chopping 2 wires on the back of your gauge cluster and ADDING a wire.
Pull off your air box cover, then pull out your air box, then unscrew all the screws holding the left rubber plate holding all the electrical junk in place (let it dangle, it'll be fine) the plastic trim in front of that should come off too since you took out the screw holding it on, that's okay because you need to get at those connectors it's hiding.
Now, you're going to want to pull your CDI (the biggest black box that was hiding in front of your air box) out of the way.
(At this point, if you don't have a beer or cold beverage, go get one because you deserve it)
Now undo the 2 nuts holding your gauge cluster in place (DO NOT LOSE THEM)
Pull your cluster loose and follow the wiring down to the 2 connectors on the front left (where that plastic trim was covering) and disconnect those so you can take the cluster all the way off, they're most likely red and white.
Now undo the nuts holding the bracket onto the back of the cluster, pull the bracket off (take a picture so you know how it goes back on) and put the nuts back on the posts so you don't lose them.
Now, take a sip of your tasty beverage as you look at the wires on the back of your turn signal light because you're going to cut them.
Leave enough room (several inches) so you can strip the casing off a bit of them (you'll probably have to unwrap the entire chunk of wires just so this part is easier. Make sure to have some electrical tape handy for rewrapping later, or some of that loom guard tubing you can get at radio shack). Here's where those rectifier diodes come in handy (you can get an assortment pack of them at radio shack for about $14 and then you'll have extras just incase you mess a few up). While you were sipping and looking at the wires you might have noticed that one is brown and the other is green... yup, they're both positive leads. Because the leds don't have enough draw (you're trying to save power while having brighter signals, right?) the extra power bleeds through this bulb into the other side of your system. That sucker is incandescent, so it works both ways! Silly yamaha, building a weak spot into the electrical system... but, it won't be able to bleed across once you're done, haha! Take that yamaha, we're adding inexpensive parts and bringing this system into the 21st century!
Pick one of the wires you just chopped on the back of the bulb and tie it into one of the grounds back there.
You should be left with one wire on the bulb and two wires on your harness.
Solder or crimp a diode onto each wire so you have a diode on each harness wire with the silver band pointed away from the wire you just attached it to because diodes are like 1 way check valves and the silver band designates the direction of flow, we don't want any nackwash. (you should now have 2 wires with diodes).
Now add your heat shrink (or electrical tape, I won't judge you) and leave a bit of the diode wire poking out because both of those need to connect to that bulb wire waiting for you to do something with. Crimp or solder that all together and heatshrink or tape it up. Now that you have that all situated, do a test and hook those connectors back up, make sure your killswitch is set to off, turn your key and test those signals. They should blink at the normal rate, and function properly (if one side works but the other side causes everything to blink/turn on, you probably put a diode in backwards, ask me how I know).
Now reroute everything back to its original place, finish that tasty beverage or crack open another and you are good to go. Pat yourself on the back and swear to never pull all that junk out ever again (until the next time you have to because you're a glutton for punishment and like adding silly parts to your silly bike).
Fin.
