Wiring: Zoeller 507 charger replacement

[Davert]

Hello, folks. My Zoeller charger is cooking batteries, and since I had a spare Battery Tender model (purchased for a van to RV conversion), I thought I'd sub that in - but the wiring is stumping me. The pump itself has three wires – two were already attached to the positive and negative terminals, but the third, from the float switch, was wired into the charger. The pump is not working now. Does that third wire go to the negative terminal, perchance?

I'd rather not blow anything up by trial and error...

Incidentally, my original research turned up this 2012 thread, which is why I'm here... https://terrylove.com/forums/index....ement-of-the-zoeller-507-backup-system.48676/