Here are your parts includes a wiring diagram.
Parts for Magic Chef CSD2123ARW Refrigerator - AppliancePartsPros.com
Sounds like drain tube is plugged so that the water from the defrost cycle cannot drain into the drain pan.
I would check that it is clear.
You will have to remove the cover in the freezer to get at it. It is under the evaporator coils.
If plugged a turkey baster with warm water, an air compressor with low pressure or a wire can often be used to clear it.
Also check that it is not plugged with dust etc. at the drain pan end.
You might as well clean the condenser/compressor fan and the condenser coils while you are down there.
If it looks like stuff is growing in the tube I would flush it with a 10% bleach solution. This should kill the stuff and let you flush it out. You may have to do this several times, let it sit for 15 minutes or so between flushes.
Be careful that the drip tray does not overflow and empty the drip tray after you are done.
Also check that the drain pan is not cracked.
Would also be a good idea to clean the condenser coils under the unit, including the condenser/compressor fan blades.
Check that when the compressor is on that the condenser fan is also on.
The fan not only cools the compressor and it's coils but also helps evaporate the water from defrost.
Also that any vents in the front kick plate and rear compressor compartment cove are clean.
Be sure to unplug the unit while doing this.
On the freezing food in the fresh food side.
Check that the evaporator/freezer fan is running.
There is usually a vent in the wall between the fresh food side and the freezer side check that it is clear on both sides.
Check your temperatures. The freezer should be 0 to 5 degrees F. The fresh food should be around 40 degrees F., thermometer placed on a middle shelf.
Check that the control actually opens/closes the damper door (Item 11 in the Controls section). This is a mechanical only damper so the freezer temperature has a large effect on the fresh food temperature.
If after all the above if it still gets water on the floor check the door seals, perhaps they are leaking and letting too much warm/moist air into the unit so you end up with excessive frost on the evaporator coils.
take a 2 inch wide strip of paper, place it between the seal and the frame, then pull it out to see how it is sealing.
If it does not seal OK.make sure the unit is either level or leaning slightly to the back.
Most units have plastic cams on the lower door hinges, check that they are OK.
Check the hinge side seal. If they grab and twist when closing the door, apply a light coat of white lithium gease or vaseline so they will slip and seal correctly.