thanks man for imfo, i have 1993 E34 525, would you wire it up any different I'm still waiting on my Z8 button, i used this one to see if i done rightThe body is the best ground. Just make sure the connection is good. Scrape off the paint if you need to, to get the best connection. Brown wire is also a good choice, but I would consider what else is connected to it, and the distance from your gadget (button?) and the point where that brown wire connects with the body of your car. Shorter is better.