I was fed up with my circa 2018 Aldi multimeter's backlight turning off after 15 seconds. I can't get anything done in 15 seconds. So! Let's hack the multimeter.

Opening it up was easy enough, remove the outer bumper, undo 2 screws, take off the backplate/pop-out stand, undo 1 more screw and we're inside.

Finding the backlight was easy, it was labelled "BL", with 2 wires disappearing under the board. Probing it showed it was drawing 2.8V, which seemed reasonable considering the battery was at 8V. I desoldered the red +ve wire from the board and extended the wire in exactly the same way everybody does but says not to.

IC3 turned out to be a handily located voltage regulator outputting 2.8V. 

Grabbing the nearest SPST switch I had I found a space where it could fit and drilled a hole with a drill press, which amazingly, was spot on first try. That never happens.

To make up for my competence with the drill, I used a circular punch to put a hole through the rubber bumper, and that was almost exactly right. I should have left it alone, instead I punched another hole that wasn't my best work.

Anyway, viola! It's now a multimeter with a switch to turn the backlight on and off! No more 15 second timeout.

WARNING! DO NOT MODIFY YOUR MULTIMETER IF IT COULD BE USED WITH MAINS VOLTAGE.