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Locomotive direction is determined by which end of the locomotive the controlling unit is coupled to it. On the rear of engines, the circuitry of pins #8 and #9 are reversed from the front MU receptacle, completing the electrical circuit in directional order. As a rule, GE locomotives usually load slower than EMD units of any model, so in a mixed consist from the two builders, an engineer has to be careful when starting a train due to the push-pull slack action between them. The selector switch others were referring to is the headlight selector switch which has five positions: 1. Short Hood Lead 2. Long Hood Lead 3. Single or Middle Unit 4. Long Hood Trail 5. Short Hood Trail, the position of the switch determined by the unit's standing in the consist and the direction it is facing. The MU2A valve was used with the 26 type brake systems when units with other type brakes such as the 24RL or #6 brake were still in common usage on many roads years ago when different type brake systems were often found in multiple unit lashups. Like the headlight switch, the MU2A valve position was set according to the type brake system on the lead locomotive. As 26 type brake systems came into more common usage, a simple IN/OUT air selector valve became the common instrument to cut the independent brake in or out of it's controlling mode. In MU operation, logically the more locomotives you have in a consist, the more problems you will have getting them all to cooperate in the starting and running of a train. It's tricky, especially with power braking where you bail off the independent brake application that builds up after making a reduction with the automatic brake. More than 6 units in an MU'ed consist will usually make for a slow bail-off release of the rear unit's brakes and if insufficient power is being used, often times unwanted buff-force slack action results. I had this problem once back in the mid-1970s with a train of something in the neighborhood of 157 empty TTX flatcars and 8 units for power, everything from an SD-40 as a lead unit, Penn Cental's lone Century 415, several GE U25Bs, plus an F-7 and a GP-9B buried in the middle of it all. And the trip was from Harrisburg, PA to Kearny, NJ, via the Northeast Corridor. If you can picture this train in your mind, you can probably understand the train dynamics that came along with it. Needless to say, the conductor and rear-brakemen were not happy campers back in the cabin car almost three miles away. As an aside, while on the subject of 27 point jumper cables...An E-44 electric had two of them in use when the units were MUed. We had some interesting happenings if the cables were accidentally reversed. But I won't get into that, as sometimes the results were quite astounding. John A. (Captain Jack) Neiss, retired locomotive engineer, Penn Central/Conrail/Amtrak
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