Trailer left blinker suddenly not working

[rb85]

Then check the trailer

[denis barden]

Use KISS
Get the trailer plug and look at the pins.
Get a small screwdriver and push it into the split of each pin and spread it apart slightly before you start doing any wiring checks.
Dont spread them apart too much as you will stuff them up
If this doents work replace car/trailer plugs .
Then you wont have a problem for years

[fishnut]

If the plug pin is an issue and its a round plug change it over to a flat type,much better especially if you go for a good quality one, I've had one for almost 10 years and no issue so far