Nothing on the terminal box. Depending on what it was originally, many of these were Lister Start-O-Matic units.
I have a couple of circuits, too big to scan.
If you can read the terminal markings on yours, I'll see if any of it matches up. Otherwise, are you handy with a meter? Tracing wires is the usual way to sort these out. I can talk you through that, if you are not confident.
My copy (only a photocopy, so no better that how it scanned) does show a resistor mounted inside one grille and a rectifier mounted in the other. Yours may be like this. Tracing wires from terminals to these bits, exciter brushes and slip ring brushes may be required.
The couple of Lister drawings here show a current transformer driving the series field. Does yours have one? (mine doesn't, but it's been heavily modified, having been found abandoned in PNG about 35 years ago by the previous owner) There are some terminal names on these drawings.
Clear pictures / terminal markings of your terminal box may help. Mine is long gone.
Jarrod.