Had to replace a broken wall switch for a hard-wired storage heater, so the mains AC had to be turned off at the meter cupboard. Some people just turn off the corresponding circuit breaker and leave everything else turned on, but I always shut down the entire house for this sort of thing. No chance of mistakes then.
I still test the circuit with a voltmeter immediately after opening it up, though.
One of my Nebo Big Larry lights did a nice job as an area light - low white mode was easily enough - and I used a BLF-348 clipped to my hat as a high-CRI headlamp for the wiring. I also had an Astrolux S41 handy for the odd bit of off-axis lighting.
While I was at it, I took the opportunity to swap out a plain fused wall plate supplying a different heater for one with a fuse and a switch. I like controllability
I don't like cowboy installers who leave insulation-destroying sharp edges on the back box, though. I swore mightily at that one. Fortunately, there was enough spare length in the cable to cut the damaged length off and redo it. I'd've been a
really unhappy camper if I'd had to put in a new length of cable.
Still got an outright dead heater to replace; I'll be using the same set of lights for that job, too