[5th_bike]

Wait a minute, did I do it right?
21W for 12V, that means there is 21/12 = 1.75 A going through each bulb.

12V and 1.75A, that means the resistance of each bulb is 12/1.75 = 6.857... ohms.

We have 4 bulbs, 2 in parallel (front and back - this halves the total resistance), and those in series (left and right - this doubles it again), so the final resistance is still 6.857.. ohms. Yes.

Now if you take all 4 bulbs out (or just both lefts, or both rights) your ohms should be 'infinity'. Please check that next. If you still measure the same 1.5 ohms, there is a short somewhere for sure.

I suspect the indicator wiring/housing. But I'm not sure about that.