My low beams on my 2007 Honda Accord are out. The high beams work, the day lights work, Just the lows don't work. I have changed both bulbs. I have checked all fuses and all relays and they are all working. How do I test the switch and how do I change it if it's bad?
If you can identify the relay for the low beam, you should hear it clicking when the switch is turned on/off.
You could use also pull out the relay and use the thickest piece of wire that you can to briefly push into the connections numbered 87 and 30 where the relay was removed from. The lights should come on while the wire is in place. If they do not, then the problem is not the switch or relay, but the connections from the relay to the headlights.
After that you will need to start taking things to bits to get to the switch.
In addition to what HandyHowie has said, I' do a bit of diagnostics. Get a multimeter/voltmeter (if you don't already have one, you should be able to get a cheap one from your local useful-stuff store pretty cheaply), set it to 20v DC, and check to see if there is a voltage reaching pin 86 of the relay when the lights are switched on - this will tell you whether the switch is working.
I'm not a Honda guy, but here's the generic info (I've done this on Mitsubishi before, same symptoms, and it was indeed a bad stalk switch):
To test the stalk multi-switch, you'll probably need to remove it so you can get access to the pins on it. On most cars this means pulling the steering wheel and airbag to get at it. This is a case where you need the OEM manual and you cannot deviate from them at all. Airbags can kill you right quick.