This makes a lot of assumptions
(switched GND, 3.3v logic level on the MPX) but it's easily altered if those assumptions prove false. It also doesn't mean I am giving up on the MPX, more of a stop-gap/alternate path.
Forgive the crudeness. I didn't use Eagle, this was done in paint.net.
The idea is to use a Teensy 3.2 to control the lights while reading the light sensor over the CAN bus. Function wise, this would be indistinguishable from factory auto lights.
The Teensy will read the three switch outputs from the stalk. If the switches DRL/Auto output is on, the Teensy will control the inputs on the MPX to set the lights on, off, or DRL. If the switches DRL/Auto output is off, the Teensy will mirror the state of the switch outputs to the MPX inputs.
All connections, less the CAN Bus, are protected by optoisolators. This should prevent us from hurting the MPX and it from hurting the Teensy.
Not shown is a 3.3V step-down converter for powering things.
In this configuration the Teensy will consume < 30mA.
If I add deepsleep tied to ignition state it would consume < 1mA when the ignition was off.