4 way light switch with power feed via the light
This circuit diagram shows wiring for a 4 way circuit with the power source at the light fixture and the switches following.
A two-wire cable (C2) is run from the light to the first switch (SW1) and a 3-wire cable runs between all the switches. The hot source is connected to the common terminal on the first switch (SW1) and the hot terminal on the light fixture is spliced through all the light fixture to the common terminal of the last switch (SW3).
The travelers run from the first switch (SW1) to one set of terminals on the 4 way (SW2) and from the second set to the travelers on the last 3 way (SW3). The hot to the light is from the common terminal of SW3 (spliced through each switch box).