What else is in the puzzle? I see brake levers. Are they connected to the brown/yellow wires? There should be a throttle with a on/off start button and maybe a LED display top show battery level? Knowing how that looks will tell a lot about the remaining connectors.

The power to the controller is the two heavy red/black wires in the bladed connector, but attaching power will not start it until you find the power on wires.

Looks to me like three 12 V lead acid batteries, connected in series for 36 volts. You should verify they are lead acid. If they're lithium, a lithium battery charger is absolutely required. Otherwise, you can charge them in series with a 36V lead acid charger, or one at a time with an automotive 12V charger.