Electrical Test Light
Electrical Test lights are just a long wires with light bulbs inside them. Here’s a crash course for using a test light: ground the clip to the frame or metal housing, pierce the wire with the sharp end of the test light, if the bulb lights up then you have power on that wire, simple and effective. They are very common and can be extremely handy for simple electrical tests. The one above (a nicer one) was less than $20, and might outlast me if I don’t do anything stupid with it. Some test lights are brighter than others which allows you to see it better and passes more current which is important when trying to activate certain components like fuel injectors. Look for an electrical test light with less than 10 Ohms resistance (you can often swap in a bulb with higher wattage, meaning less resistance), but don’t be too concerned because this is often not specified on the packaging and will most likely work just fine for 99% of your tests. I’ve linked a few possible options below.