I purchased a 2015 Skoda Octavia MK3 diesel NHS ambulance, and I'm in the process of stripping away the extra electrical components. The responsible for converting it into an ambulance had removed the spare wheel and installed a battery in its place. My goal is to remove the extra wiring and reinstate the spare wheel. I began by unplugging all the cables and removing the additional battery. However, now facing the car won't start. The front displays the correct voltage battery (I've tested it), all the lights, both internal and external, are functioning alright, and the windows are operational, but the engine won't start when I turn the key. Does anyone have any ideas on how I can tackle this problem?

Face away from the vehicle, its shy! 😄

Going down a slippery slope. I'm not sure which one will be a leisure battery or, if they're all connected, to power the lights while stationary.