It's always a tricky thing to try and pinpoint the first of anything. The first working automobile, the first powered flight, the first beer of the night — all these things are usually surrounded by an impenetrable haze of uncertainty and occasionally, vomit. Often we can make some pretty decent guesses, but this time I feel pretty confident in making an out-and-out statement of what I think is fact:

The first vehicles with on-board electrical communication systems were Civil War Telegraph Wagons.