rachelh, GFCI = Ground Fault Circuit Interrupter. You don't really need to know how it works, just that if something happens, it can save your life. GFCI outlets should be tested monthly. There should be two buttons - TEST and RESET. Plug a small lamp into the outlet, turn the lamp on then press the TEST button. The RESET button should pop out and the lamp should go off. If that happens, press the RESET and you are fine. If the RESET button pops out and the lamp does NOT turn off - get an electrician in to check the outlet. It is wired incorrectly and will not protect you in case of an accident. See the top three (and probably more) of the links in the Google search below. GFCIs could save your life or that of a loved one. Here is a link that might be useful: Google GFCI search

Most likely the connector(s) and/ or wiring is at fault. Check the connections at the lights first to see if there are any exposed bare wires or if the incorrect wire connectors were used. If there is no problem with any of the connections, the next step is figuring which section of the wire has been compromised with an ohmmeter (circuit assumed unplugged).

This is a common 'trick' for large loads like motors. By bringing out more of the motor windings from the stator the device can be used at more than one operating voltage. It increases the complexity of the windings though since they must be divided into appropriate sections and then the terminals made available. The same thing s done with motors designed for 120/240 V operation (not "high voltage" at all). It has littler to do with branch circuit wiring topology. You will notice we do not have 120 V bulbs and 60 V bulbs. This is what would be required to have some portion of alighting circuit in series and some portion in parallel. I personally do not do production wiring and use crimps for much at all. You will learn to dislike them when you start doing remodeling work and are no longer doing all 'new work'. I do charge extra when I am forced to deal with remodeling that has crimp connections. Simply cutting them off is often not an option since the remaining conductor length often then violates the minimum length required from the face of the junction box. I am sure it speeds up the 'production' installers though. Right now I have a house with a built in on one side of a wall, and a tile backsplash on the other in a kitchen. I need a couple new circuits for under-cabinet lighting. It looks like I will have to go through the back of the kitchen cabinets and fish upwards to the new junction boxes in the back of the upper cabinets. At least there are no crimps present in the boxes already containing some lighting switches.

Testing for presence of live AC voltage aka (Plug any device into a string of general purpose 120/volt 15/amp outlets from a dedicated circuit breaker and the electrical power is lost to all the other outlets on the same string? Unplug the device and the power is restored to every outlet on the string? This happens to every outlet on the string not just one no matter where you plug or unplug any device. Hum wonder what the heck is going on here?) discovered burnt wire operating on 1 outlet that was back stabbed burnt off it also had a antique hanging light plugged into a outlet in a clothes closet with brittle cracked lamp cord wire and still in operation? hum the plot thickens. Back stabbed devices (outlets & switches) are a weak link in connection virus tapped true series circuit, along with mixing outlets and lighting on the same circuit breakers. AC electrical power 200 amp main breaker 120 240 volt single phase from utility grid will always take the least resistance to ground thru rod or rods if properly grounded. Older ungrounded residential wiring that needs upgrading is usually beyond repair and is a candidate for a true series circuit pigged tailed according folded grounded upgrade for a new wiring harness and devices to local, current codes and standards and inspections.