It also depends on the definition of "new". If it's a week old, I'd say it's very likely a short in the system somewhere.... with the operative word being "somewhere". You are correct in suspecting the switch. Always start with the question "what has changed?" and the switch is probably the only thing changed from the original charging system.
If the battery is a couple of months old, then water levels are probably the #1 suspect.
On the other hand, it's really easy to check the water levels in the battery, at no cost to you. Start there. If they are good, start ohm-ing things out, starting with the switch.