Yamaha nouvo z, front left signal light is steady, no back left signal light, right side signal light all ok, what is the problem?

SOURCE: Signal lights on R1 don't work...

Though I can't recall what the wire colors are for your bike's turn signals, here's how to figure it out: on the turn signals that you bought, first determine which wire is the ground by removing the light bulb and then checking to see which wire has continuity to the turn signal's metal bulb socket base.
Then find out which wire is the running light and which is the turn signal by hooking the ground wire and one of the other wires to a 12 volt power source. Which ever wire makes the brighter part of the bulb light up is the turn signal - the dimmer one is for the running light.
On the bike, match the turn signal wire to the bike's wiring that is 'hot' with the turn signal switch on. Plug the running light wire from the turn signal into the bike's wiring that is 'hot' whever the key is on. Hook the turn signal ground wire to the bike's ground wire(s).

Testimonial: "Thanks so much. Your advice about checking which wires are "hot" with key on or signal on makes perfect sense."

SOURCE: 1995 yamaha blows more exhaust on the left side than the right

Assuming the bike idles smoothly and is not smoking you can pretty well rule out bad valves and piston rings. If the air filter is clean then intake should be okay. Are the valves set properly? Is the decompression lever and valve working properly? I assume there is not mud plugging up the pipe. That pretty much leaves the muffler on the right side having an internal collapse and is restricting the flow of exhaust gases. Remove the mufflers and see if the pressures are equal at the head. If the problem is still there then have the shop do a compression check. It is possible a ring has broken or is frozen in the ring groove. This would let some compression into the gear box and account for the lower exhaust pressure. I hope this helps.