You will need a voltage meter and a a fuse puller. Basically pull the fuses 1 at a time and put the meter in series and it will show you the current draw on which ever circuit that's causing the drain. For me it was my after market head unit. to be more specific it was the memory wire. I don't know why but when I removed it the current drain stopped. With my wife's z it was the after market viper alarm and remote start. There is actually a write up on the specifics on how to trace this problem.