On Thu, 12 Apr 2018 08:19:04 -0700 (PDT), Terry Schwartz
wrote:

That can easily be addressed by using two LEDs in parallel, in opposite polarity.

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

Although this tester is shaped like a pen with a needle point (made to
puncture wire insulation) and a wire with a clip on the end. I normally
use the wire as the ground (to any metal part of the car body). But I do
like the idea of putting two LEDs reversed polarity in there. Easy
enough to do...