How much does it cost to have the wires replaced under the hood?

There is no available estimate from this published - you'll have to get a real world quote from a local repair facility near you. https://repairpal.com/repair-shops/ford-repair-and-service-in-stockton-california Based on wires "taped together" and "some of them touching metal" - I'd be highly concerned of a fire hazard; that said - evaluation of the vehicle is strongly recommended, as wire repairs are often much more cost effective than harness replacement. Furthermore, you don't know if the concerns you are having are because of a wiring harness issue.