StuCam

Hi everyone I have a parasitic battery drain in my 2013 Octavia estate. Following the instructions on a you tube video I was able to find the drain which was a constant 0.5A when the car was shut down and asleep. I pulled every fuse an relay on both fuse boxes while measuring the drain with an ammeter between the negative lead and the battery terminal. I couldn't isolate the drain to a fuse or relay and was about to give up when I noticed the cover on the front of the engine fuse box which covers a buzzbar with 7 leads connecting to the battery positive terminal and 6 leads going to parts of the engine. so with the meter measuring the drain I disconnected each lead in turn to see if the drain disappeared and when I disconnected the thick black lead the drain dropped from 0.5A down to the 0.03A that you should expect normally. So I left this lead disconnected and checked if the car would start which it did!!!! Turned it off while I put the tools away intending to take it for a test drive but when I tried to start it again I realised that I had flattened the battery........sorry to leave this on a cliffhanger but is there any smart person on here who can identify what this lead feeds to and how critical it is. The Lug has the letter G stamped on it if this helps to identify it on any wiring diagrams. Thanks for any help Stuart