Well even though you did not do anything to the electrical system, some common causes of this behavior could be electrical in nature so rule out the easy stuff first - 1. Check all the fuses. 2. Check the voltage at the battery terminals with the engine running at idle speed (650RPM) - you should have 14V if the alternator/voltage regulator is working right. 3. If you haven't replaced the OVP relay but have only changed the fuse, it would be a good idea to do it now - a lot of starting problems originate from a bad OVP relay - the internal solder joints corrode over the years - I have one that I recently cut open from my 1989 300E and at least 6 joints were clearly broken (desoldered) because of heat and frequent switching cycles.