A well devised EMP device causes ground current. Even shielded and "grounded" systems can be reached for an event unless they are grounded in a very deep counterpoise design. The ferric nature of the geography dictates the shielding requirements and sometime, possibility or improbability of a defense.
Most EMP knowledge has been acquired through testing in the 1950s and still holds true for the most part today.
If the electronics of modern automobiles are largely immune to EMP, so too can other electronics be protected.