GM always made sure the taillight wires were protected from unexpected damage! Because vinyl covered wires were not yet invented, the cloth covered wires required extra protection. This is certainly true for wires in the wheel well area that are continually hit by road debris.
This was done by a 5/16 diameter inch galvanized metal flexible conduit. The length was different between the ½ ton and 1 ½ ton which depended on the distance from the back of the taillight to the factory hole in the frame rail. See Photo. All made in the USA.
Good News: This kit is available especially made with flexible conduit crimped on brass ferrules on ends and the curved metal connector that secures it to the oval taillight. This connector must be used to correctly attach the wires to the original oval taillight.
Different length on 1 1/2 ton.