Today I worked all day trying to get the left landing light on my Comanche 180 to work. I tested for voltage and it appeared to be a bad ground. I know this because it tested voltage present when I selected a better ground. I wire brushed the ground wire, checked continuity on the bulb, even though it tested okay, I tried a new bulb. Still no luck. As I mentioned, at one point I had voltage. I finally gave up with intentions of trying again some other day. Any ideas, or thoughts?

Rick. If you know you have a good ground then You might want to check your landing light switch in the cockpit. If the contacts inside the switch are corroded over
it might let some current through, giving you a positive indication of voltage, but as your lights draw a fair bit of current there would not be enough current
through to light the light.

You could test this out by exercising the switch several times and checking for results. (sometimes works for a little while by "rubbing" the corrosion off the contacts in the switch) If that doesn,t help try the same procedure with the circuit breaker as it also can be a problem area.

Those are the easy checks... next would be the wire continuity check from the light lead to the light switch. Take the wire off the switch it should be labeled L1B from the left landing light switch and then take off the wire L2B from the right landing light switch. Connect the wire L1B to the right landing light switch and then see if your left landing light works by turning on the right landing light switch. (you know your right landing light works, so by using the switch and power from the right side to power up the left side, you will now know what the culprit component is)
If your right landing light works, then you have a bad right landing light switch or circuit breaker, if the light still doesn,t work then you have a bad wire from the switch to the terminal block in the wing root or the wire from the terminal block to the light.
Try this out if you are confident about the procedure I just outlined or have your AI do it for you. I would also double check your ground before doing this as the ground problem seems the most logical.

Hope its just a ground problem or a simple switch replacement.
Let us know what you find.
Good luck,
Gary