US flight time limitations (FTL’s) often require a third pilot as do the UK ones hence the 3rd driver. The “fuses” mentioned earlier are actually circuit breakers. There are some switches over there too but are only operational on the ground. It was set up to satisfy the unions but there was no retrofit to change anything. I regularly fly some of the first 757’s off the production line (Eastern was the original customer) and they don’t even have a seat there which is a feature of most other 75’s. The 767’s difference is only that the 3rd seat is always fitted.