Mercedes Benz C320 2003, key don't turn in ignition, have to manually unlock car, checked fuse box while car running, switched off, the all malfunction lights went on, disconnected battery, now the key won't turn, display lights only on when you put headlights on. Interior light not working husband checked cockpit fuses and in engine whilst car running, when switched off and ignition turned on, console light up like christmas trees vir malfunctions, disconnected battery.
When attempting to start car, the key does not turn in ignition at all, alarm not working as well.
Check the battery cable connections where they end at. The ground will terminate at the engine block and the positive will terminate at the starter. Check them for a tight fit and see if there is corrosion which would cause problems. Clean off corrosion or tighten bolts if needed.