Yes; an air connection and an electrical jumper.
There were two air throttles available; the older D-1 Controlair, and the newer CE-100. They were NOT compatible with each other. The D-1 was used for single unit and multiple unit applications; the CE-100 was required for units with dynamic brake. The two throttles differed in the range of air pressure applied to the throttle pipe, and in the fact that the CE-100 employed an internal switch to close/open the main power contactors. The simpler D-1 just admitted air to the throttle pipe; a separate pressure switch tapped into the pipe detected proper pressure and shut the main power contactors.
While I'm at it, neither of these was compatible with the air throttle fitted in Fairbanks-Morse units --- and the F-M units had two different cam fittings for two different pressure ranges (30 lb and 60 lb if I recall.)
And, while I'm STILL at it, you COULD get an electric throttle (Westinghouse XM-781) in the Baldwins that could be arranged for compatibility with other units using electric throttles.
Above is the page on my website showing these various controllers.