Today I diagnosed it, and found that even with hazard lights, the right bulbs front and back don't light up. Swapping the bulbs left to right at the front and back still don't light it up. So that eliminates the bulbs as the cause.
I pulled out the flasher unit like what the other threads and miata garage recommended. Here's a picture of the back-side. Could the upper right corner have a faulty solder? There's a black spot on the board and on the 2 nearest solder drops.
EDIT: Anyway I can get it resized?
