Electrical – Fuse blew, outlet didnt work, replaced outlet, still not working

It's possible you have a short. From your question I don't know if you disconnected D by removing the connection at C or D. You could try this:

I'll assume since you did all this you're basically OK working with electrical. Get yourself a non contact voltage detector and use that through this whole process to confirm things are dead before you touch them.

• With the breaker off, and the switch off, look at the wiring in the box at D. Look for any place the bare conductor of the hot wire could touch the bare ground wire, the neutral, or metal inside the box. Look for nicks in the wire, places where stripped wire extends past the wire nut, etc.

• If that doesn't reveal anything, with the breaker and switch still off, remove the last light fixture (D) and cap the hot and neutral wires with wire nuts. Turn on the breaker, turn on the switch, see if it trips. If so, there is probably a short between the hot and neutral wires or hot and ground wires in the cable between C and D.

• If it trips with the D light disconnected and the wires capped, turn the breaker and switch back off, remove the C fixture, undo the wiring and cap the wires that feed D, and reconnect C as if it was the last light in the line. Turn the breaker back on, turn the switch back on, and confirm that the breaker doesn't trip.

If it does, then something's not consistent. I'll assume it doesn't.

• Turn off the breaker and switch again, and test for continuity between the hot and neutral wires from C to D, and between the hot and ground from C to D. If you see continuity with the wires disconnected and capped at both ends, you've found a short. The wire from C to D will have to be replaced.

If this doesn't lead you to a fix, you might want to call in for reinforcements, and leave that breaker off until they arrive.

First thing to check, as @Tester101 points out, is that you've connected the wires to the LINE terminals on the GFCI receptacle. It will also have LOAD terminals, which would go any other outlets you'd want fed from (and protected by) this GFCI. But it doesn't appear that you have any of those.

Next you should carefully use the contact terminals of your multi-meter to measure voltage on the lines:

• If you measure around 120V between the black and white wires leading to the GFCI, and those wires go into the LINE terminals of the receptacle, the receptacle should be test/reset-able and should show 120V when you test between the plug-in slots on the front. If you have 120V at the LINE terminals and not at the front, the receptacle is defective.

• If you don't have 120V between the black and white wires, your circuit is switched off or damaged. You'll need to investigate the wiring to determine what's wrong. Your non-contact tester may have given you a misleading indication; the contact tester is more authoritative here.

• To identify the "true" neutral, measure voltage between an insulated wire and the bare ground wire. Neutral and safety-ground should have zero voltage, because they are bonded in your main electrical panel. So you should have 120V between black and white; 120V between black and ground; and 0V between white and ground. If you have 120V between white & black but 0V on black/ground and 0V on white/ground, then your ground wire is not properly connected.

Finally, you should run a small length of bare wire between the ground bundle in this box and the ground screw on your switch, so that the switch's metal components are grounded.