Agree ...get a digital multimeter. Protect your circuits, and yourself.
If you have a couple extra bucks, you can get a multimeter tester with a clamp-around loop to measure dc current running through the wire, without having to stick the leads in series.
Search "clamp dc current digital multimeter"
Most low priced clamping meters only measure AC current, so read the specs to find one that has both AC and DC current (uses a Hall effect trick of inducing a magnetic field) measurement using the clamp.
I have the Klein Tools CL2000. I see it listed online for prices ranging from $100-120 tonight. Has helped me track down both DC current gremlins in cars, as well as 110v AC current in the house and underground sprinkler valves that use 24v AC.