u/CommercialSignal7301

I’m including pictures, hopefully for clarity. I’m installing a Bbs02 mid drive on a recumbent (my second such build). I bought the kit used and when I turned the system on with the original battery, the display would activate, but immediately go blank. I happened to have a spare 48v 12ah battery, so mounted it, fully charged. Now the display doesn’t turn on at all. I double checked the battery at its cable and at the butt connectors and both showed 52volts. What would be the next thing to check?