I have a 2003 Ford Focus. The problem we are having is the high beams work with no problems BUT the low beams will come on at all. The fuses are ok & have been replaced. The bulbs have been swapped out. But the low beams still do not work. Has anyone else had this issue? Any suggestions on what I need to look at to fix this?
If you get the same behaviour on both sides, and you have twin-filament bulbs, then my first suspect would be the switch. If they are separate bulbs then I'd suspect earth connections (as per Mike's comment).
We can break the circuit you're testing into several distinct parts:
(1) Battery -> (2) wire -> (3) fuse -> (4) wire -> (5) switch -> (6) wire -> (7) bulb -> (8) wire -> (9) earth.
We can assume the first three are fine (you've tested the fuse), and you've changed the bulb (always worth testing the new bulbs too, just in case!).
Get hold of a multimeter, and work your way backwards along the circuit checking for voltage/continuity - I'd probably start with the connection on the back of the bulbs first. Use the 'continuity' function on the meter to check that you've got a good connection from the earth pin (usually a black wire) to the battery negative. This tests 8 & 9.
Then use the 'voltage' function to check that you get 12v on the high beam pin when highs are on (which you should, as you know they are working!). Now switch back to low bean and check the other pin - if it's working, you should see 12v there too, but if there's a failure in the switch or wiring then you won't. (Testing 1-6 all together)
Assuming that the earths are fine, and there's no voltage on the low-beam pin, then the switch is our next suspect. This next bit can be difficult, just because of access! Get hold of a 'Haynes' manual or similar, you'll need the wiring diagram to identify which pins are which. Remove the shrouds around the steering column to get at the back of the switch. If you're lucky (I don't know the Focus), there might be a connector somewhere near the fusebox you can use, otherwise you'll have to disconnect the one on the back of the switch.
Use the multimeter to check for continuity between the power feed into the switch and the low beam wire coming out with the switch in 'on', 'low' position (5). (for peace of mind, again check high first, so that you know what you should see). Also check for continuity between the low beam wire here, and the other end of it at the bulb connector (6) - you'll need a long length of spare wire and an assistant. If you've got continuity there, and none in the switch, you need a new switch. If it's the other way around, then you've got a break in the wire.