A feeder assembly of a car sliding door has a protector in which a wiring harness is arranged for electrically connecting a car sliding door side with a car body side. The assembly includes a generally circumferential wall positioned inside the protector and an auxiliary unit disposed within the wall, the auxiliary unit connected to the wiring harness. A resilient member resiliently urges the wiring harness within the protector, and the circumferential wall also serves as a stopper to limit the bending of the resilient member. An outside harness insertion hole and an inside harness insertion hole are formed in the wall, the outside harness insertion hole leading the wiring harness outside the protector, the inside harness insertion hole leading the wiring harness inside the protector. The circumferential wall has a bottom deeper than a base pate of the protector. The inside harness insertion hole is disposed between the bottom of the circumferential wall and the base pate of the protector. The auxiliary unit is secured by a fixing means and a locking means.