[prob.: from SF slang for an electrical-brain-stimulation addict]
1. A hardware hacker, especially one who concentrates on communications hardware.
2. An expert in local-area networks. A wirehead can be a network software wizard too, but will always have the ability to deal with network hardware, down to the smallest component. Wireheads are known for their ability to lash up an Ethernet terminator from spare resistors, for example.