A car turn signal flasher relay can be externally tested to find out for sure where a turn signal problem is located.
To test a turn signal flasher relay, we can use an external 12V source or simply the 12V car battery.
We must feed the flasher relay with 12V - be careful of the polarity, or we can damage the relay, since it has internal electronics.
To close the circuit we use a 12V lamp connected on one side to the negative of the source or battery that we use, the other end of the lamp is connected to the free contact of the flasher relay or flasher.
Once we have tested that the relay works well, we must go on to check the wiring and fuses to locate the problem of the flashing lights.