Can not remember witch way my ni-cad connector goes into my receiver

[Gunner49]

I have a Airtronics 92765/72 receiver and ni-cad battery pack and had to replace the connector on the ni-cad pack. In the process I forgot the polarity of the connection. The only thing I remember is that the red wire goes in the middle.
Can someone remind me which way it goes. The receiver has three pins, but the ni-cad pack has only two wires.
I think that if I connect backwards, the receiver will be toast. I have attached pictures.
Which wire goes to what pins? or of the three pins, which one is the hot pin, and which one is the common pin?
Any help will be greatly appreciated.

[Gunner49]

Update on my problem.
I found a section in an old manual that explains it clearly and now it works.