http://www.van-cafe.com/home/van/page_775_810/automatic_neutral_safety_switch_kit.html

Couldn't this piece be used to wire up an alarm to make a noise of some kind when you park a vanagon, like an initial pleasant beep if you did the right thing and put it into Park, and warning alarm if you don't (with an override switch)... I can't count how many times I've had to thrown it into park after jumping out of the vanagon only to notice it starting to roll. One time in particular was really scary, on an incline... 

They can do this, 
http://www.van-cafe.com/home/van/page_764_810/battery_saver_alarm.html so it should be able to have this added feature. 

I don't understand electronics enough to pull it off myself... I'm still puzzled over the Shunt for my solar panel and how it would work with a second battery.