They normally have a place in the engine compartment to jump start the engine if the battery is in the trunk. If you cannot find it, check your owners manual: http://repairpal.com/automobile-owners-manuals-online
By: Shahram Azad - Windermere, FL
Open the hood of your car, on the driver side, next to the fuse's box, there is a rectangular ( 2 3/4 inch by 1 3/4 inch) cap, 2 little lock pins on each side of the cap, lift the lock pin to open that cap. This is the positive + terminal. Connect this terminal with the + of a GOOD battery, on the negative , you can clam the jump cable to anywhere that have a good contact. At this point you can jum start your car & you can open the car's trunk, because there is juice connect to you car now. I am Owner of 1998 C280 Sport and worked for me. Good luck.