Seriously! I really hunted the answer for my troubles with a display for my Arduino. I know for a fact that it's blue, backlid and has four lines of each 20 characters. But...
I've identified the added chip as an I2C and wired the pins according to various online sources. Should be correct.
I've attached pictures of wires, chip and sketch/errors.
When I treat it like 2x16 characters I get a blank blue screen.
When I treat it like 4x20 characters I get a black screen as the light turns off.
I neither case I get any letters, symbols or anything of the like.
Help would really be appreciated here, thanks!