I guess the Electronics button on right side is just a show on/off the usage of electronics, it doesn't turn the electronics on/off, that might be configured using the game setup.
Ok, i thought i can use the Mclaren P1's DRS. If you notice my image you can see a DRS botton at steering wheel and a dashboard blue light DRS indicator.It's green all the time because you are in a street car that doesn't have to conform to DRS rules. (which is new in 1.4)
Take the Lotus 125 S1 to Monza and you will see the green icon turn grey at the end of the straight.