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Neighbours threw out a gorgeous lamp, which had broken by the socket becoming disconnected from the wires. My housemate brought it home, and I tried rewiring it. Following an internet tutorial, I figured out which wire was hot and which was ground (necessary since I want to put LED bulbs in) and then wired the socket back in. Voila, it works... sort of!

The lights are really dim - subjectively like at most 10% as bright as they are in a different lamp. Tried both LED and CFL.

So I figured maybe I can finally put my engineering degree to use and bought a multimeter. Sure enough, resistance through the bulbs seems to be about 2 milliohms, but from the plug to the socket, about 300-500 milliohms. That would explain why the circuit is mostly not lighting up the bulb!

(Come to think of it, this would also explain why, when I tried testing which wire was hot and which was ground using a coin cell battery and a tiny standalone 5V LED, it worked with just battery & LED, but not when I tried to run the circuit through the lamp wire.)

...but what do I do about it? What's a likely source of the issue? I suppose maybe we could keep the lamp fixture and completely replace the wire & footswitch...

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    Using your meter, lamp unplugged, measure resistance from the neutral prong to the shell of the socket, and measure from the hot prong to the center contact of the socket - that's how they SHOULD connect, anyway - and operate the switch while measuring (which SHOULD affect the hot side only, but who knows in this case.)
    – Ecnerwal
    Sep 24, 2020 at 21:57
  • 500 milliohms (1/2 ohm) is not a high resistance. A 100 watt incandescent bulb draws less than 1 ampere so that this resistance would drop less then 1/2 volt, not enough to affect the bulb. LED lamps draw considerably less so this does not explain your problem. You need to look elsewhere. Also LED bulbs designed for AC mains power do not care which lead is hot and which is neutral. They will work either way.
    – Barry
    Sep 24, 2020 at 22:32
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    Try a plain incandescent, i.e. borrow one from the lightbulb museum. This clears an amazing number of problems relating to dimmers, motion sensors, and other things that power themselves in series with the bulb. Incandescent bulbs are non-linear and are extremely low resistance when off. Some controls rely on this.
    – Harper - Reinstate Monica
    Sep 25, 2020 at 0:05
  • re-measure with the meter leads swapped, there may be a diode in the wiring somewhere.
    – Jasen
    Sep 25, 2020 at 11:57
  • @Harper-ReinstateMonica as I understand it, the moratorium on incandescent bulb sales has been lifted! It's possible (though still not likely) that one can find new incandescents for sale!
    – FreeMan
    Sep 25, 2020 at 12:50

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Likely is a bad switch, or a bad connection.

Unlikely is "high resistance wire"

And if you are planning to "put your engineering degree to use" please learn the difference in line connected items between "neutral" (Grounded) and "ground" (Grounding - safety ground - whole different thing.)

Your safest bet if low on real world experience is to rewire it as low-voltage DC. That way if you spork it up nobody gets hurt. Far too many internet tutorials are terrible, and if you don't know enough it's hard to sort the terrible form the good, and terrible can be quite unsafe...

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    I like the low voltage idea. since it's an old lamp, all the wiring in it should be replaced... get a little construction in there with that engineering degree. +1
    – JACK
    Sep 24, 2020 at 22:26
  • It's not an old lamp, as far as I can tell. Just second-hand. Looks like it might have been bought new in the last few years.
    – MalcolmOcean
    Sep 26, 2020 at 1:24
  • And yeah, I know the difference between neutral and ground haha, I just forgot the word for neutral when I was writing my question. I'm mostly used to just "positive" & "negative". Thanks for pointing that out.
    – MalcolmOcean
    Sep 26, 2020 at 1:25

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