So, the stock harness and switches are expecting voltage (+) to be run through them, and the MU input is only expecting a ground (-) to come to it. Stock, the LH switch gets power to it from the GREY which comes the flasher unit. You need to re-wire the whole thing like this:
I have a white wire (to light on mbutton - this will only work if the MButton is installed within steel bars. Otherwise, ditch the whole thing.)
Brown and blue - Abandon Stock, its the Turn Signal Buzzer
Orange and white - Abandon Stock, its the Turn L indicator on cluster
Blue and white - Abandon Stock, its the Turn R indicator on cluster
Orange (left blinker) - TURN L on MU
Light blue (right blinker) - TURN R on MU
Orange and white - Abandon
Light blue and white - Abandon
Black and yellow - Tie to frame ground
Brown and white - Tie to frame ground
Gray ( blinker relay ) - Tie to frame ground
Light green ( Horn ) - HORN
Dark blue (light ) - Abandon
Wiring it this way, the LH switch will now only send a Ground signal to the MU. Powered wires run from the MU right side directly to the component. Make sure the MU is setup for 5 button, Japanese style controls.