General aviation pilot reported running the aircraft off the taxiway after trying to follow a faded yellow taxiway line in dark lighting conditions at SDM.

Narrative

It was a very clear dark night without moonlight. Upon clearance for taxi; I followed what I thought was the taxiway centerline as I kept track of the blue taxiway edge light on the left. It was very hard to see in front of me as the plane had very dim taxi/landing lights; so the front was not well illuminated. The yellow taxiway line was also very faded so I thought I was keeping track of the correct yellow taxi line. There was a big gap in the blue taxiway edge light; and it was not continuous; so I mixed it up and mistakenly thought the taxiway curved as I saw that the edge of the taxiway was now on my right. In seeing that the edge was on the right; I continued taxiing; keeping the blue edge light to my right this time; but I ran off the taxiway.The cause of the problem was my mistake in believing that the edge light switched and stayed on the incorrect side.No damage to the airport or airplane was done. And no one was injured. I believe what can be done is that if the plane's light is too dim; I should not continue with my mission; especially on a non-moonlit day.