Connections between cars for push-pull operation?

When operating in a push pull system what connections need to be made between cars with cables?
Thanks

Usually there is a control cable with 7 or 8 wires, an HEP cable with 4 wires and a communications cable with as many wires as are needed for the service. The latter may not reach the locomotive. There are also two air pipes, a fixed pressure control pipe and the usual brake pipe.

4 hep jumpers with 4/0 wires(red)
One 27 conductor Traction jumper (black)
One 27 conductor Communications jumper(blue)

Good grief. I'm startled that the number of separate cables hasn't yet been reduced by a standardized combo plug design. I guess every time a new feature was added, historically, it got its own cable.

I remember reading Farnk Middleton's "The Interurban Era" that the trolley companies very early on used couplers that would make physical, electrical and air connections, and I'm pretty sure that's the norm with light rail equipment. Does anybody know how prevalent that is with light rail, subway-elevated, and railroad, mu or push pull, and why does rairoad, or at least push pull still have so many separate connections to make?

[quote]Does anybody know how prevalent that is with light rail, subway-elevated, and railroad, mu or push pull, and why does rairoad, or at least push pull still have so many separate connections to make?[/quote]

I'm told WMATA has a ?29? pin connection, air, and maybe another power one on existing cars. The new cars will be a fiber-optic connection, period. {Maybe also air, don't know...] So they will not be intermixable.

But why are automatic connectors so prevalent on light rail and subways, but not on regular FRA type railroads?

[quote="gardendance"]But why are automatic connectors so prevalent on light rail and subways, but not on regular FRA type railroads?[/quote]

Perhaps because they break/assemble consists much more often?

For the most part, push - pull coaches have to be able to couple to whatever switch engine happens to be in use in the yard, thus the standard AAR couplers. Since there is slack action in such couplers, jumper cables are superior to contact buttons. CTA had a tight-lock knuckle coupler on its cars, but these only coupled to similar cars. They may still be in use there.

Automatic couplers are only good for trolleys and or MU cars. The coupler does make air connections and low voltage control connections but can not handle tracktion or HEP power.
on Push pull equipment the two 27 pin jumpers one is standard 27 pin MU jumper, the other is a 27 pin ( differnt turned head) communications jumper for all non traction control connections.