I changed the bulb though it was good still. I changed the switch. From the breaker box it goes; bathroom light, hall light, bedroom light, porch light. All other lights work just fine.
First thing I would do is check the bulb on another verified working fixture. Sometimes even two bulbs are dead so you thought it wasn't the bulb. If not, then:
Next I would see if there was power coming to the wires that connect to the the light fixture.
But note that you need to test the wires going to the fixture, not just the fixture itself. You are ruling out the fixture as the cause of the problem.
If there is power going to the wires connecting to the fixture (with the correct light switch on), then you have found your problem - the light fixture itself.
Third, if power is not going to the wires that attach to the fixture, then you know at least that it is not the problem, or not the only problem (the fixture could also be bad, but you have another problem somewhere else as well if no power is coming to the wires).
- So, the third thing I would check is whether there is power coming to the light switch. If there is power going to the wires connected to the switch, then the problem is somewhere between the switch and the light fixture.
If there is not power going to the wires connected to the light switch, but like you said the lights are wired in serial (one after the other), then since there IS power going to the bedroom light like you said, which you mentioned is the fixture before it, and the switch is wired in serial AFTER the bedroom light fixture, then your problem is the wire between the bedroom fixture and the light switch for the porch light; or, perhaps the wire is detached from the previous fixture.
That should be a good starting point. If there are only wires between the light switch and the fixture, and between the light switch and the previous fixture, then one of those wires is bad, if you have gotten to this point in troubleshooting.
If it is not in serial like you said but wired in parallel, then it is a little bit more complicated to find, but it should be pretty intuitive from here and this it a good starting point for you either way.
Update: I made a quick photoshop for you to help visualize. This is of course assuming it is wired in serial like you said in the same manner, but this is effectively how you will go about troubleshooting. Just change it a bit if it's wired differently, but this should answer your question fully.
I put a question mark with an arrow to the points of failure. It could be
- the part connected from the previous fixture (could be disconnected, etc.)
- the wire to the switch
- the switch itself
- the wire to the fixture
- the fixture itself
- the bulb itself
You asked in a comment above how do you test if there is power going to the wires? Well the unsafe but easiest way is simply to attach a wire to the wire to the positive and to the negative and the just put the two wires to a working light bulb (side and bottom of the light bulb) to see if there is power going to it.
Here is a quick photoshop of this hack. Please use common sense and don't shock yourself. If you do this, screw each loose wire on top of the other wire, ON the light switch where it screws onto it. This will prevent the wire from flopping around. Be sure to put electrical tape on the loose end of the wire so they don't hit each other while you/re getting situated and blow the fuse or shock you while hanging.
If it lights up then the wires are fine and it's one of the things between the switch and the porch light. If it doesn't light up then the problem is either the wires or the connection to the previous fixture.
You can also test the voltage with a voltage meter but may not be necessary, although this is the better and safer way.