If it's AEG, and Fisher-Price then it's probably that famous Mattel quality control at work (or lack thereof
).
Still, I second what's been said already, it's probably a loose wire, and if so, you'll have to pop it open to secure said wire again, otherwise I can't say I'm sure exactly what to suggest.

Still, I second what's been said already, it's probably a loose wire, and if so, you'll have to pop it open to secure said wire again, otherwise I can't say I'm sure exactly what to suggest.
Been building Plarail worlds since 2001; Building when I can in 2023 
