Air carrier pilot reported poor runway hold line markings and lighting resulted in confusion over runway hold short instructions at MDSD/SDQ Airport.

Narrative

After landing in SDQ on Runway 18 even though we could have exited safely at D we were told to taxi down the runway exit at G taxi Runway 17; then hold short of 18 at H due to an unavailable gate and congested ramp. As we approached Runway 18 on H we were unsure of where the hold short line for 18 was. There are two now blacked out hold short lines. There is a hold short sign. I informed Tower I was unsure of when I should stop; and if they were comfortable with where I was. They asked if I could see the hold short lights. We could not. After holding short for a while we were able to scrutinize the 2 blacked out lines; hold short sign; and identified the hold short lights in the pavement though they were not illuminated. We were indeed short of what we surmise was the hold short line. However; in light of day it was confusing with the hold short markings/lights not appearing as expected; it would be incredibly easy to miss at night especially with rain and end up past the hold short line and on Runway 36.