I want to add an outlet in the middle of a run in the garage. The start of the run has a GFCI outlet with the proper line/load connections. The 2nd outlet in the run is a regular 20A outlet. Can I a new 20A outlet after this 2nd 20A outlet but before the 3rd 20A outlet so that it becomes a 2nd ending point to this circuit? This allows me to just run one set of romex to the new outlet instead of having to run two. Thanks.
You can wire an single additional Romex from the 2nd electrical box off to a 4th for outlets. Just make sure that you use the proper gauge wire (should be 12 AWG for 20A circuit).
If the current 2nd outlet is wired in a manner where the incoming wires are attached to the one set of screws and the outgoing run is connected to the other set of screws on the outlet then you will have to do a little juggling around to accomodate the added outgoing run. I would suggest to remove all current connections off that outlet and use good quality wire nuts of the correct size to join all the live wires (blacks), three from the Romex cables plus a 4th pigtail together. Do the same for all the neutrals (whites). The pigtails would connect to the 2nd outlet to connect it to the circuit. Lastly all the safety grounds (bare or greens) need to be wired together, connected to the box and to the green screw of the outlet.