Seatbelt ticket

I saw fight it. You have absolutely nothing to loose and this idea that "the cop is just doing his job" or "has to enforce the law" is BS. LEOs have discretion, especially when it comes to moving violations. For example, if you're cruising down the highway to 8mph over and a cop clocks you at that, he's under no obligation to pull you over. If you're going 12 over he may pull you over but still doesn't have to issue you a citation. He can give you a verbal warning, a written warning, or write you up for a reduced violation. In PA there's something called "failure to obey a traffic control ordinance". It's cheaper than the lowest speeding ticket and no points. Finally, they could write a speeding ticket for a reduced speed, thereby lowering the fine and points. Again, it's called discretion. The cop was probably having a bad day. Or, maybe he's just a dick.

Bottom line, you were in at least partial compliance by wearing the lap belt. Your intent was to comply with the law, you just didn't realize you were also required to wear the shoulder belt. It's said ignorance is no excuse, but in the end we're all human and judges do realize this, especially if you're an otherwise upstanding and productive member of the community. I'm not saying you'll get off scott free, but based on my experience with traffic court, it's definitely worth the effort.