How to diagnose if sporadic turn signal functioning is signal flasher or signal combo switch?

Question

Symptom: When activated by the turn signal combo switch, turn signal goes on for about 5-10 seconds, and then turns itself off. Turn signal combo switch remains in the on position, but the turn signal stops. The symptom is sporadic: sometimes it works correctly, sometimes it does not; sometimes the symptom is only in one turn direction, sometimes both.

Research: Research indicates that it is most likely a faulty turn signal flasher or the signal combo switch itself.

Question: Besides replacing one and seeing if it fixes the problem, is there a way to determine which part needs to be replaced?

Answer 1

Since its sporadic it is more annoying to troubleshoot, but you should be able to check for voltage after the combo switch and see if that is consistent. There should be continuous voltage to charge the flasher (from my understanding of how the flashers work) to charge the flasher. If there is stable voltage when the blinker stops blinking, then there's probably something wrong with the flasher. Could be a bad cap or relay, but it's not even worth opening it up to find out. You may save a few buck fixing the flasher, but you'll lose twice what you save in time spent. :)

Now, if your vehicle is outfitted with LED blinkers this changes how the flasher functions, but unless they are factory LED blinkers, the above should hold true.

Answer 2

If you are lucky, there is a separate flasher for the emergency flashers that uses a similar relay. If so, just swap them and see if the issue is fixed. Or you may swap one from another car, just to test it.