On a full WOPL, 2 speaker ground wires run from the DCP to the buss bar. In the photo, these are the two white wires that come off the DCP and go down. The red wire on the DCP goes to the rectifier, the black to the buss bar. The yellow wires you see at the DCP are the + outputs coming off the backplanes, right and left channels.
The light bar pcb is powered by wiring that's incorporated into the transformer, should be a loose pigtail coming off the transformer. The meter signals come off the backplane in a WOPL, not sure about original wiring, probably off the backplane. Additionally there is one extra voltage wire going to the DCP that is green in the photo, think this is B+, but I'm on the road, on cell, can't check.
Good thing is you have a original 400 to look at that should help at this stage. Hope this photo helps even if it is a 400. Hi Res, should be able to zoom in, the light bar wiring should be clear along with the DCP grounding.