Abstract: A crawler device for pulling a leader string through electrical or cable conduit. The crawler device has a traction head, for example using caterpillar-type rubber tracks, biased outwardly into contact with the inner wall of the conduit when inserted in the conduit. The traction head pulls its own motor and power supply behind it, serially and flexibly linked to follow the traction head and negotiate curves in the typically small diameter electrical conduit. In the preferred from, the power supply is a series of linked batteries, such that the crawler is an independently and self-sufficiently mobile machine traveling through the conduit.