I got the left blinker light up whenever it rains heavily. I removed the interior cover of trunk, but did not find any water. I cleaned up the tray below windshild and warpped the harness with tape. It works finally.

 

I found that the problem still sometimes comes up. I checked the tray under windshield after heavy rain. There were two water flow dropping into engine room. I have two solutions.
1. Pasting a long tape inner side of the plactic cover as picture.
2. Filling 2 holes with silicon on the cover.

The water is falling in these two points.

1. Pasting a long black tape in inner side.

The tape is like the green part. The water would not go to the gap anymore.

The water is coming out from the water tray.

Filling up this 2 small holes with silicon.