A cord was not supplied for the '98 e300s, all of which I understand have block heaters. The owner had to request one, which the dealer supplied without cost. At this late date you have to buy one. The dealer charges a lot; NAPA charges less. There is a Wiki paper on installing a cord.

I don't think you need a block heater. I've gone though ten winter with temperatures a few times around 5 degrees and many days below 20 degrees. The car has always started easily. The previous owner lived in Philadelphia and did not use it. The wiring has never been installed on my car.