I went to start my car the other day and I discovered the turn signals were bad..that just wouldn't blink.
I did 2 hours of troubleshooting, jumpering the flasher relay and the emergency flasher switch and working with DVM and couldnt get the system to function. I followed the circuit diagram from point to point and my anaylsis made complete sense.
I suspected a bad Flasher switch since thats the heart of the system and i could fire my flasher realy with a 12VDC power supply.
Nothing worked, until I accidentally disconnected the cruise control switch harness instead of the flasher harness. Suddenly the Flasher system came back to life.
It did make some sense since the Cruise Control switch was "Limp" and had lost its mechanical integrity, but I did't think that it had failed electrically. But basically it made no sense at all! As I said How come Electrical Troubleshooting is never logical?

Because electricity is PFM.

Electrical troubleshooting is perfectly logical.

However, it's quite complicated and the fact that many components are grounded will really confound you.........unless you're very skilled at isolating the suspect.