Track tester lights.
A friend of mine that passed away about 25 years ago had some storage cabinets that his son gave to me. I found this track voltage tester with a light and some metal tabs on the bottom (only took me 25 years to find it!). This would be a very cost effective way for making a track tester. My more expensive one (around 15 bucks) gives audio and visual test plus how many volts are present.