What could be causing this???

Ok, I have a mazda B2600 that I have been having trouble with. I turned the key to "start" and when I turned the key off the starter kept cranking. I had the plugs pulled on the engine so it was turning over easy. I ended up pulling a battery cable off to get it to stop. Would this be the main relay? I pulled the main relay and took it apart and it looks fine?. My original problem was no spark, I just replaced the distributor because it was in bad shape. I tapped on the main relay and then I had spark and then the starter issue accorded.
Does anyone have any ideas?
Thanks

Sounds like an ignition problem to me

Sounds like you might need to take the starter off and have it tested. Maybe the solenoid is getting stuck.

There is no relay between the ignition switch and the starter.
If battery voltage is low, the starter solenoid does not throw quick/hard enough, causing the contacts to weld together. The only other cause that I can think of would be the ignition switch is failing... which mymmeryloss alluded to.