The difference is that a highly mechanically modified car is a fairly understandable system. I write embedded firmware for robots for a living. I've got a fair

The difference is that a highly mechanically modified car is a fairly understandable system. I write embedded firmware for robots for a living. I've got a fairly good grasp of the complexities of a system like this. These modifications terrify me. How does he know that one system isn't talking the n-1 protocol which is incompatible in subtle and weird ways from the current one? How does he know that there isn't calibration data hiding inside one of the systems he installed which assumes a different dynamic response? Systems engineering for a system of this complexity is really really complicated. Bugs develop in the interactions between systems even when every part is working fine. If you start glueing stuff together which isn't designed to work together and is relying on unpublished unversioned APIs for communication, you're going to get all sorts of problems.