There should be a male quick disconnect terminal sticking out of the back of the clock. That is your positive battery connection. Grounding can be provided anywhere on the metal chassis. You can use the clock feed from your mercedes or simply hook it up to a good battery (even a fresh 9 volt should work). If using a car battery put a 1/2 or so amp fuse in line to protect yourself and the clock in case of a short circuit. Hope this helps, John.