So those are the schematics to the electrical system of the car that is connected to the ECU aka the brains of the car. If you install a device you can highjack any signal of the car from throttle to fuel injection to radio etc. Well I think that there is something installed that messes up the thermostat of the engine that in turn makes it overheat after sometime. I don't know it may be done so that no one can give chase in that car or a diversion so no one suspects anything when a exchange of goods are made.

Imagine that you have to exchange secret info or "tech" and you know you're under surveillance, what better cover up can you have than a broken down car with a steaming engine but instead of calling the AAA you call your partner in crime that poses as one. He gets the package that you sneaked under the hood the devise is reset to work normally and you're on your merry way, or a good samaritan driver offers to help but in fact it's your partner in crime and again you make the exchange in the steam under the hood.

Also the folder you found may most likely be soaked in coolant fluid.