Ft Wayne Interurban Combine - Unterbody parts

Only few images exists from the Fort Wayne - Lima Interurban Combine, and the unterbody parts are hardly to see on them. Fortunately, better photos exist from the mostly identical Indiana Service Corp cars.

On one side we can see
1 - a fuse box reverser box
2 - a four bloc resistor grid, with perhaps the 3rd position empty
3 - a drawbar
4 and 5 - air tanks

On the other side there are
1 - probably the compressor
2 - an unknown small cubic device
3 - the brake cylinder
4 - an unkown device with a chain
5 - a square box, probably the switch box

Does anybody have further information about this parts? What is the unknown device #4 with his "bicycle chain" ?