Just to verify Ben, can you take a picture of the motors? Most all Williams diesels use two Mabuchi 385s. A few of the early ones only had one motor. Stall current with two motors is under 6 amps. That is worst case. I am not sure anyone here really knows what E unit you have there. Most all Williams units use relays even the ones from the '90s. K-Line Conventional E Units use transistors and its common for those to fail.
Bottom line, get a newer Williams E Unit and you should be fine.
Pete