Fuses came up during the Second Squidwrench Electronics Workshop, so I’ll bring a handful along to the next session. Conveniently, the doomed Sienna’s rear storage compartment disgorged a new-old-stock box of fuses, along with a fuse puller/tester containing a pair of
feeble vintage 164 / LR60 / AG1 alkaline cells:
Somewhat to my surprise, the other side of the PCB has components:
It looks like a transistor switch to minimize the current through the fuse and protect the LED from over / reverse voltage, should you apply it to a live circuit.
A pair of new cells had it working just fine, not that I expect to need it in real life.