This procedure is for the 911SC, but the other 911s are similar.
If your engine has a hard-to-correct miss, it may need a new set of spark plug wires. In some cases, when the wires are bad, you can get quite a light show when you open the engine lid at night. With the engine running, you may see sparks jumping from the spark plug cables. Another indicator of bad wires is if you get a little shock when you touch the plug wires with the engine running (be careful of the fan and AC belts).
It is a good practice to replace the distributor cap and rotor along with the wires. These two parts aren't expensive, and replacement of them will ensure strong ignition. You can assemble the plug wires to the new distributor cap before installation. That makes it easier to observe how the old wires are routed around each other into the distributor cap, and how the braided ground straps are routed around the wires. When assembling the wires to the cap, apply a thin coat of dielectic grease on the end of each wire, around the outside of each nipple on the distributor cap and coil, and inside the end of each spark plug connector. This will ensure good electrical contact, and help with disassembly in the future if it is necessary. Be sure to orient the new distributor cap the same as the old one, and to insert the plug wires in the cap in the correct firing order.
This is also a good time to replace the spark plugs if needed. Do not use any anti-seize or lubricant on the spark plug threads- it can cause a plug to back out.
After you assemble the new wires to the new cap, remove the two air hoses (one plastic and one paper/wire) on the driver's side of the engine. Then unfasten the two hose clamps along the top of the engine cooling shroud, and the clamp that holds the paper/wire hose onto the heater blower at the driver's side of the engine. Move this hose (the one that goes across the top of the engine to the passenger side) out of the way to allow better access to the plug wires. Unsnap the old distributor cap, and remove it along with the old wires, by carefully pulling them out from below the intake runners. When removing the old wires from the spark plugs, it may help to rotate the plug connector first to break its seal with the spark plug, and then pull off the connector.
Install the new rotor, seating it firmly and in the same orientation as the old one. Install the new cap, making sure that it is seated in the notch on the distributor body. Route the wires in the same path as the old ones, and attach the ground straps as before. Carefully insert the spark plug connectors, observing the firing order of the engine (Pelican Parts plug wires have the plug number stamped on each wire, to make installation easier). You should feel each connector snap into place onto the end of the spark plug. Reinstall the air hoses, and you are ready for a test drive!
Bob at Pelican Parts