I was purchased two M200 thruster. After soldering and isolating the cables, i was tried to check the thruster for isolation in the water (using isolated tester) .
Unfortunately the tester showing zero ohm resistance.
Okay. That looks like it should be well sealed. Can you please try the insulation test again but lower the motor into the water slowly and watch for a change in resistance. You may be able to pinpoint the area with the issue that way.
If you can pinpoint a location I can offer recommendations to fix it or we can replace it.