Corrosion may still be your problem or a broken wire. If you have a corrded terminal or a broken wire with a strand or two touching it will still check out with the ohmmeter and read volts also as the meter uses a very small current, but not enough to light the light and "pulls down" to nothing with a heavy load like the headlight. Use a long wire running from the headlight fuse or relay to the light to see if that is your problem, then go along the current path with that wire till you find where it stops working.
To check for broken wires, tug on the ends while holding the wire, bad areas will "stretch" under the insulation. My favorite is scotch-brite for terminal corrosions, my pocket knife for really bad ones.