Lots of people put them on the knee bolster, right side, but I figure when I need to get to it is not going to be the time that I want to be bending down to reach it. I have mine in the left side of the upper cubbyhole in the dash. I have it slanted slightly toward the driver. When and if you need to reach it to apply full trailer brakes, you need to be able to reach it easily. Just my $. 02.....