I've put together this circuit, and (with some help from EE SE) it's working great.
I have it wired like this: where the diode comes first off the middle transistor pin, and then the motor negative comes next. The motor negative lead and diode are not touching (except that they're in the same vertical rail).
I understand the diode is in this circuit to handle discharge of the 12V solenoid. If I wire the negative lead first, as so: would this be equivalent to the above or does it matter where the diode is in relation to the negative lead?