My 85 500 SEL has some strange quirks. recent engine change and the mechanic replaced the elctronic fuel/idle regulator (?) because the car would not idle smoothly - it kept racing up and down. After that was replaced, I thought the car was fixed but when I tried driving at night, the car revved up to about 2000 rpm when I turned on the parking lights and when the headlights were turned on, the car simply died. The low beams and fog lights do not work although they all look like they should. Had the alternator and battery checked and they are good. I tried disconnecting the fog lights and that made the problem worse - it won't stay running at all now. Any suggestions woudl be helpful. Previous owner said he did not have these problems so I am hopeful there is a simple explaination/solution.

 

you try looking at the overload protection relay yet? It's one or two usually 10 amp fuses. cheap, but can cause issues like that when it goes.