I created your design with some changes.
I used a DPDT relay I had in my junk box.
As an Electrical Engineer who used lots of 7805 voltage regulators in noisy environments it would be a good idea to use a 1uF filter cap at the input to the voltage regulator and a 0.1uF filter cap at the output. The 7805 are prone to oscillation when using long wires at the output. You can actually use a 78xx as an audio amplifier to drive a speaker! Just put your iPod to the regulated pin and a speaker to the output pin and you can get great fidelity audio. In the lab we used 7812 and got 8 watts RMS of audio power.
You do not need a potentiometer/trimmer just use a voltage divider using a 22ohm resistor and a 560ohm resistor and power both DME pins on the relay.
I get 0.196V which is close enough to 0.20V.
Now a question to all of you. I have an M56 SULEV engine so there is a secondary air - air mass meter. How do I deal with this????? Anyone figured this one?