Can't ground my lights! Help

[RPurdy]

I bought some general amber lights from the store. They have a wire for power and "self ground" by running a plate to the screw whole so when the screw touchs it, it grounds the circuit. Well I screwed them in and just wired them into all my other running lights. However they aren't working and Its the ground. I tested the wires with a test light and the wires have power. However when I put the test needle up to the screws the light lit up. Indicating the screw running through the two wholes for mounts are hot. And they are screwed into metal. The screws shouldnt be hot though because thats the ground right? The rest of my running lights are working and I know each light is receiving power. Even when I unscrewed them and put a screw driver against the metal plate on the back that grounds it, it still didnt light up. Any help would be appreciated. Im no electrician.

[Chop]

Use your test light backwards to check for a ground.Just clamp your lead onto the positive side and begin testing for a good ground.If you have juice at your ground,you should be popping fuses.Sounds to me you have a poor ground which juice flows thru the bulb giving you the "hot "ground

[RPurdy]

So the ground is poor probably. This is causing the power to "flow" through the bulb and not illuminate it? I honestly will admit I painted the plastic base black to match what it was up against. I figured the screw would scrape enough paint off to make it ground able. Ill try what you suggested but in the mean time would it help to scratch the paint off on the metal plate in the screw whole?