I had a similar problem on my '89 740 Turbo. The headlights and front sidelights kept intermittently shorting out. It was a result of poor ground wiring. Look above the wheel well on the driver's side there is a small dull gray metal bracket set up to receive several ground wires. Make sure this is clean and that all connectors to it are clean and well attached to their respective wires. The problem I had was that a previous owner had clumped too many wires onto a single ground wire attached to this bracket. Once I spread the wires out across the bracket, cleaned everything up and shielded all of the bare wires with shrink wrap or electrical tape all of the shorting out problems I was experiencing went away.