if you are not comfortable of making the harness you can always buy one. even in europe, lots of places just make it for you. like $6-10. steps to check
1. plug one battery into harness and check output connector for right voltage
2. plug other battery into harness and check output connector for right voltage
3. plug into controller hopefully controller is fine
Hopefully... yeah.. It's ruined atm. The seller is trying to help me. He may replace it, fix it, or guide me to fix it. I can't really solder, but I'd rather do it myself because of time.
I am fine with working with electric things, since I love electricity. And this was a stupid mistake not to check voltage. I took the electrican guy's word on it that it's parallel. But it's clearly not. The positive is connected to the negative...
Do you know the name of that connector? I want to buy a couple of both. Or, even better, the name of the connector on the controller?