On Thursday, April 12, 2018 at 1:54:15 AM UTC-4, wrote:
I have one of those general purpose 12V auto testers. It came with a
tubular incandescent bulb, about the size of a 3AG fuse. The bulb burned
out, and I am not going to waste a lot of time trying to find a
replacement. The whole tester cost about $15.

But before I toss it, I got to thinking that all I really need to do is
open it up and wire a LED inside of it. Pretty basic. I think the LED
should outlast those bulbs too. I have a bunch of LEDs, but none have
the built in resistor.


At the risk of pointing out the obvious, an incandescent bulb doesn't care which end is positive. An LED on the other hand..................