Well im not sure about a "trnsfer cable" but alot of the 2002-up GM products require a bypass-modual to work with the factory theft system, Airbags, Door chimes etc..? So it is very possible that YES he may require this unit to properly install a new H.U. I have seen it done without the modual and you do not "NEED" one but i highly recommened it for warranty and safety. If I remember correctly, they ran around $169 CND but I could be wrong. I hope this helps a little bit!