My New Holland 3630 has a new battery for a month. When the key is inserted into the switch, the lights come on. But when the key is turned to the on position the lights on the dash don’t come on.
The first thing to check is all the fuses in the cab and engine compartment. With the key in the “off” position, and you sit on the seat, the dash lights should come on. If so, the seat switch is fine. When you attach the seat belt, the seat belt light should go off. If not, you have a problem with the seat belt switch. These switches and the frayed wiring to them are a common problem. Do you have an error code? You will need a service manual to troubleshoot the system.