Turn signals-one side works,one doesn't

[Laban87]

1981 Yamaha XS400. My right turn signal works most of the time but my left one barely works. Sometimes neither does. This problem just came out of nowhere. Any thoughts or advice on why and how to fix it? Thanks!

 

[bcware]

Can you describe what you mean by "barely works?" Blinks fast? Blinks slow? Doesn't blink at all? Stays lit?

 

[BBS360]

#1 Check the bulbs. A loose filament could still work occasionally but need replacing.
#2 Check the connections through the wiring harness for both sides. Make sure they're all tight and corrosion-free.
#3 Take apart the handlebar switch. Dirt and moisture can get inside. The left signal contacts could be dirtier than the right.

 

[XSLeo]

Nothing "Just comes out of nowhere" There is always a reason. As mentioned dirty contacts are most likely the problem. Not only check the power side of thing, check the grounds.
On the sockets the bulbs go in, they can stretch open and le the bulb vibrate in the socket, this can allow the contact points to burn as the power arcs across the gap. Clean and tighten every connection you can.
I might suggest you do this not only on the turn signals but the entire bike. Start at one end and work to the other. Switches, connectors fuses. Everything.
Leo