The plugs at the bottom of the Central Electric Panel are identified by letters, left to right, so C is the third plug. The connections on the plug are identified as two-digit numbers, with the first number showing left or right side of the plug (1 left, 2 right) and the second number showing the connector bottom to top.
 
 

Therefore, C23, C24 and C25 are the top three connections on the third plug from the left end.

Wally Plumley

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Be careful with the top retaining clips for the plugs - they are very brittle - if you stress them too far upwards they will snap off. Best way to remove the plugs is to make a puller tool - a paperclip works. The plug bodies have 2 diagonally opposed tabs that stick up with a small hole in each. Open up the paperclip, bend the paperclip into a U shape, then bend a small hook into each open end with pliers. Pop the hooks though the tabs and then you can pull the plugs out straight from the panel with one hand while easing the retaining tab with a flat blade. Don't pull on the wires.
Alan.