Its essential that you determine which black wire is hot before proceeding. The black and red wires are both hot and each is connected to one of the receptacles.

Home Wiring Hot Wire
I have 2 black wires and 2 white wires outlet. In this diagram two outlets are wired in the same box with a separate 120 volt source feeding each. However if you need to rewire a light switch or a plug socket you may occasionally come across two black wires. So can i extend the black and white from the existing 2 wire receptacle to new location and install a 2 wire outlet or gfci outlet but leave the romex ground not connected at each end. On 2020 03 04 by mod where do i connect ground wire when i only have two wires. Basically the procedure is simple. Three wire cable runs into the box.
It is common to feed thru an outlet in other words to bring the power in on one trio of wires tied to the outlet and send it out on another trio of wires also tied to the outlet. The easiest and safest way is to use a multimeter to test for current. You then repeat this with the white wires with a short length of white wire. But in that box there are 3 sets of wires going into the box there are red and white wires twisted together white and black twisted together and actually the main power wire going to the light switch i am wanting to change which has a black wire white wire and a little single lead wire going to this light switch twisted together. At the wall switch connect the black wire from the new piece of romex to the bottom screw. The white neutral wire is splice to each outlet so they share the return path.
Black means hot white signifies neutral and green indicates ground. If the fixture has leads connect the two existing white wires to the white lead. Thanks for asking robert lets clarify this question. You take a short length of black wire roughly 6 8 inches of the same gauge as the wires in the wall then you take your two blacks and you twist all the ends together and marrette them. Wiring 2 outlets with 2 sources. Connect the two existing white wires at the light fixture to the silver screw of the light fixture.