The hang up with the pulse is that like you said it can fry electronics not plugged in. The chances of a circuit unplugged being effected is relative to the ciruitry and its capabilty to conduct power. The length of the harness is an equilalent to the secondary side of a transformer. With the circuit unplugged the amount of h field energy coupled is small. The harness of the vehicle however would be subjected to the h field and effectively couple the energy to all circuits connected to it. That is what happens to the power grids in solar flares. The power lines get the current induced on them from the Magnetic pulse generated then carry the current back to the transformers and electronic controls and knock them out. If you disconnect then you can lessen the impact and chances of failure. All electrical wiring become a transformer in a magnetic field. Lighting, alternator, ignition coil and will tranfer power. The diesel idea keeps getting thrown out there. Yes a diesel with a mechanical injection or carb would be better then the electronic controls but you still have wiring, and alternator and they would see the effects as would anything hooked to them like an ignition, Depending on the field generated....even the diesel has potential issue.