Review on SunFounder I2C LCD Module Shield for Arduino R3 Mega2560 - 2004 20x4 Serial TWI by Brian Motley

This display works well with the i2c interface connected to the Arduino. However, I did find that the 2 backlight enable pins on the interface board were shorted even with no jumper installed. This made it impossible to adjust the backlight brightness, which was too bright for my application. With great difficulty I was able to separate the interface board from the 1602 display board, allowing access to the underside of the interface board where I was able to confirm that there was indeed a trace connecting the two backlight jumper pins. Trimming the trace restored this jumper's original purpose, allowing you to control the backlight (with the addition of a series resistor). Be sure to check if your jumper doesn't affect the backlight. Keep in mind that the repair will take a lot of time and patience as you will need to desolder all 16 pins connecting the two boards.