Bob R Wrote:
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> Was there a published standard for getting all the
> locomotives from different manufacturers hooked up
> together, and, if so, when was it developed and
> put in place? That's what they refer to as "MU"
> connection, no?
> What train functions did it involve?

Not sure that I understand your question, so if this isn't the answer you're looking for, ask again.

There is a large cable with 27 pins that electrically connects all units in the locomotive consist. It's called an "M.U. cable" and as a very basic description, it causes the training units to do whatever the lead unit is doing, sort of like if you plug stings of Christmas light together.

There are a number of air hoses between the units that basically operate in the same manner as the M.U. cable, but for air functions such as braking.

If you take a look at these two of Martin's photos that he posted a couple of days ago . . .

[www.railroadforums.com]

[www.railroadforums.com]

. . . you can see the air hoses on either side of the coupler. The one on the right (as you're looking at the photo) that's closest to the coupler operates the train brakes. The other hoses are for the locomotive's air system (the two outer hoses operate the sanders and were used when older units are in the consist; on newer units the sanding is electrically operated). A couple of the hoses are missing, but you can see where they'd be.

Just above the platform across the front of the unit are the recepticles - they have round lids on them - for the M.U. cables. The one on the right is for a 27-pin cable. Directly above it is a rectangular-looking plug for the Field Loop cable that controlled the dynamic braking on older units. On the left are two recepticles mounted vertically. They are for the 12-pin and 21-pin M.U. cables, which was a system UP used primarily on older units. If you could M.U. all the units in the consist with 27-pin cables you didn't need to use the 12 and 21-pin cables. Eventually, the 12 and 21-pin recepticles were removed and the 27-pin system was used exclusively.

I'm not sure what you mean by a "published standard." The Association of Americal Railroads (which is the Class 1's lobby group) has a lot of rules, but I don't know if there are any regarding M.U. The 27-pin M.U. cable has been the industry standard for many decades, but it was common back in the "Old Days" for different locomotive manufacturers to use different M.U. systems, or even different M.U. systems on different locomotive models.