Help with 12-hole rack tail light for Elgin

[mpdoan2]

Hi! I have this Elgin I got for my wife. It has a 12 hole rack and a tube for a tail light, but just the tube. It appears to fit 2 D sized batteries (like the headlight and horn) but I don't know what pieces I'm missing, if there are any available, or what it should look like when all together. Any help would be greatly appreciated.
Thanks in advance!
Mike