I'm just thrilled to see SOMEONE who doesn't call it a "cellanoid".
I agree, its more likely a relay. In addition to the big terminals, there should be two smaller ones, a + and - (or just one, if it grounds through the mounting bracket). Should be infinite ohms across the two big terminals until you apply voltage to the little one(s), then should go to 0 ohms. If it doesn't, the sucker's broke, and you have to get a new one- no way to fix.