Over the last few weeks my left turn signal had become intermittent and then finally quit working altogether.
When it quit working, what I observed when the left turn signal was switched on was:
a) no turn signal flashing
b) the left front the turn signal not on
c) the left rear turn signal is on steady, not flashing
d) the left turn signal indicator light in the instrument panel was constantly on but dimly illuminated.
This is what one typically would observe if a bulb has burned out and created an “open circuit”. Since the signal indicator light is illuminated, it is also a direct indicator of power at least as far that point.
If I pull the headlight switch out to “park” position, both the front and rear, left and right parking lights come on. Also, since both front parking lights come on with the headlight switch in the “park” position, the problem most likely is not a ground problem. If there was a bad connection between the socket and ground, one would expect that neither the parking lights nor turn signal lights would function properly.
First thing to check was the front left turn signal/parking light bulb. When I removed it, both filaments looked good. I confirmed that the bulb was good by using a multimeter and checked for continuity between each two contacts on the bottom of the bulb and the metal side of the bulb. Bulb checked good. The problem is not a burned out light bulb.
For the next step, both the front left and right turn signal/parking light bulbs are removed.
Next I turned on the parking lights and checked for voltage between the left socket contact and ground on the driver’s side. I also made this measurement on the passenger side. In both cases, it was essentially 11.5 vDC, which is what I expected since both of the front parking lights were functioning properly. I turned the parking lights off.
I turned the ignition switch to the “ON” position and turned the left turn signal on. I measured the voltage between the right socket contact and ground and on the driver's side got 0 vDC. I turned the right turn signal on and made this same measurement on the passenger side and got 5.5-5.65 vDC.
(Note: when looking at the front of the car and at the parking/turn signal light socket, the parking light is the left contact and the turn signal is the right contact. Refer to Photo #1.)