OEM replacement wires already have everything they need if you ran them the same way as the factory did. However, you can use plastic split corrugated wire loom jackets to slip around any area of the wires that lays on the engine or otherwise needs to be spaced away from the other wires etc.
http://www.allelectronics.com/make-a-store/item/SLT-38/3/8-DIA.-SPLIT-LOOM-TUBING/-/1.html