I have an '84 300 sd. It runs well but the battery drains with the key off. If I put a volt meter between the batt terminal and the connector 12 volts is flowing through the system. Obviously there's a short that's causing the problem so I need to find it. What is a good systematic way to find it? A good electrical schematic would help. Where is a safe place to download an electrical diagram for the 1984 w123 300sd? Thanks for any advice.