WHAT is the best way to tie my arduino ground to the car's computer ground.
Electronic cruise control can easily be built for under USD 10 in parts.
That's why a commercial cruise control costs USD 300 to install in your car, while it's maybe USD 10-20 worth of electronics.
The vehicle's ground is the chassis. just tap into anything structural with a 10/32 and a ground pigtail and your in business.
I do not intend on using it on a regular basis.