Step 1
Remove the drywall panel above your doorway or window to gain access to the header. Use your crowbar to pry the edges of the drywall panel away from the studs and header, and use your screw gun or hammer claw to remove the drywall screws or nails. (Reference 5)
Step 2
Use your hand-held router to notch a groove into the header wide and deep enough so your power wires can pass through. Only cut as much as necessary, and start with a shallow and narrow cut, expanding as needed. Attempt to fit the wire after each attempt to avoid over cutting. Once the wire fits into the groove, you must cover and protect it.
Step 3
Install flat metal nail-protector plates over the wire, and the notch to prevent nails and screws from being driven into the wire. Each plate has metal spikes at either end. Use your hammer to drive these spikes into the header, and use your screw gun to install drywall screws through the metal plate screw holes.
Step 4
Install a new drywall panel over the header and studs. Use your screw gun and drywall screws to fasten the drywall panel in place.
If possible, avoid cutting and drilling doorway headers when running wires. Remove the door frame trim, and try to fit the wires through the adjustment or shim space between the door and the header. Use your hammer and chisel to shave away the edges just enough to fit things through, and leave the header out of it.
Use a stiff wire and tape -- sometimes called fish tape -- to hold and pull power wires through your hollow walls when headers and studs are not in the way. Wrap the end of a piece of wire with duct tape. Push the wire through one wall opening, and out of the second wall opening. Attach the power wire to the stiff pulling wire with the duct tape. Pull both wires back through both holes to run the wire along the path you need.
Use caution when working with electricity. Never work with a live line. Make sure the right circuit breakers are tripped, and that all the lines in question are dead before beginning any work.
Try your best to notch all load bearing headers toward the top of the wood beam and not the bottom. Try to avoid notching headers near existing knots, and do not make your notches more than a quarter of the way through the wood.
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