ELectrical problems
 

The other day my 75 450 SL was running fine. I parked it for a few hours and then it wouldn't start. I think my fuel pump went bad (haven't had time to check it yet) as I don't hear the little noise it makes when the switch is turned on. My major problem occured when I was trying to start the car. I would run starter for a short period and at times the starter would keep cranking even after I shut the key off and took the key out of the switch. I had to disconnect the battery cable twice. Is the ignition switch bad or where do I start looking for that problem? The starter was replaced a month or so ago.
Thanks