If you make a closed loop it does not matter what you have plugged in because you are not checking through those devices. You are just trying to make a "closed circuit" between the "one" wire you are testing. Electricity takes the path of least resistance and you will have, technically, no load between the L14-30 and the extension cord.I did do the test earlier with all breakers in the on position. Looking at the diagram - I need to turn only one breaker on. Unplug anything in the sockets and turn off any lights. Plug in a regular 110v extension cord and test between the 110v extension and the generator 30A extension.
1. Yes, at first you want the L14-30 plug you connect to the generator in the circuit through the inlet box. This will have all the "parts" together as in what should be normal operation. Then once you run in to things that are not correct start peeling back the layers of parts and check/verify those. As @iowagold mentioned - commercially made cables may still be worth checking over to see if they are, in fact, correct.Two questions:
1). Do I need to test with the 30Amp gen cord plugged into the inlet box or can I test between the prongs of the inlet box and the 110v ext cord?
2). I am only interested in readings from ground to ground, neutral to neutral and hot to hot between the 110v ext cord and gen cord, correct?
2. Yes. That is the purpose of the cord being there. The most important part of the testing is to get your Neutral correct on the generator cord side from the L14-30 to the breaker box. With the wiring question in the inlet box (between it and the breaker box) - this is likely where your issue is and why you're going through all these "hoops". The Hot wire of the extension cord (black, the narrow blade on the plug/socket) should only connect to one of the hot pins on the L14-30 - if everything is wired correctly. There again, if it isn't and you are loading up neutral somewhere along the lines - that is exactly what you are trying to test for here - to map out the connections/wires as described in the brown box with yellow text in the diagram. If it is too hard to read copy the picture and save it to your computer then zoom in. On my web browser it doesn't let me zoom in to the image, only the base website/text.
Keep in mind that ground and neutral will be bonded together both at the generator and breaker box. So you should have continuity between ground and neutral. The important differentiation is between Hot and Neutral.