Agree with adjusting if there is a screw on the outside. Contacts are pretty big and healthy inside. Before taking apart I would shock it several times with bursts of 12V. This is provided you are 100% sure you have it wired correctly while load shocking. I would also "knock" it around a bit, like vibration mode, with a dead blow hammer. Usually no wiring inside, just "stuck" contacts. Not fused together, just corroded. Taking it apart won't hurt it unless you are a relative of Little Lulu.
