Procedure: box with two (2) cables (4-6 wires):
(a) Detach one cable's white wire and hot
wires from the receptacle and cap each
one separately with a wire connector.
Make sure that they are from the same
cable.
(b) Re-install the receptacle in the electrical
box, attach faceplate, then turn the power
ON at the service panel.
(c) Determine if power is owing to the
receptacle. If so, the capped wires are the
LOAD wires. If not, the capped wires are the
LINE wires.
(d) Turn the power OFF at the service panel,
label the LINE and LOAD wires, then
remove the receptacle.
(e) Go to step 7B.