im glad you mentioned that. I was fairly confident there was no ready made device for my car so I never even looked. I just googled it and came across a site where a guy made a simple circuit that made the TC default to off.
**broken link removed**
I'm not sure what the resistor is for though. He mentions- "The computer sees the switch as closed when the resistance between those pins is less than 9K ohms, and open otherwise. "
There is probably a good reason for the resistor, but I know nothing of electronics.