Possible causes of problems with a vehicle's headlight switch include a faulty switch or blown fuses. Additionally, there may also be problems with the switch's wiring. Headlight switches incur a great amount of use, so they tend to fail over time due to usage as well.
To identify a problem with a vehicle's headlight switch, take the time to rule out that it is not another fuse or an improperly working headlight relay. Check for blown fuses and replace them, and if the headlights still do not come on, use a voltage meter to make sure power is getting to the fuse. If it is, remove the headlight relay, and shake it to see if there are any rattling noises. If it rattles, replace it. If not, put it back in; the lack of rattle indicates that the relay is working properly, but no power is getting to it. Therefore, it may be a headlight switch problem.
To test the headlight switch, remove the switch from the instrument panels so that its wires are exposed. Attach a jumper wire from the switch to a voltage meter to see if power is coming to the switch. If it is not, use a wire piercing probe to test each individual wire to identify the problem. If only a few wires are not receiving power, replace those wires. If none of them are receiving power, replace the entire switch.