which wire is the line and which is the load on trigger switch?

Depending on where you live...

On the power cord... into the switch...
In Europe Line is Brown - in the USA it's Black
Neutral Blue and White respectively.

Out from the switch...
Load will be a wire that goes from the switch to the motor - generally but not exclusively the same colour (color) as the Line (live) coming in.

If you wire up back to front it will make little (no) difference.

Good Luck...
July 2016