So I took apart a photocell switch (turns on exterior lights automatically when it gets dark) as it wasn't working, figured it might be the photocell that's the problem, internet search says you test them by measuring resistance across it and shining light on it.
In darkness - high resistance, with light, lower resistance.
On mine, with light - resistance in the megaohms. W/out I get null (Infinite resistance?). Is it broken? Or is that what it's supposed to read?