I have a 1999 ford explorer sport and low beams not workiing.

Change the headlights to Low Beam and it will switch off.

2003 Ford Explorer - Dealer E Process

dealereprocess.org https://cdn.dealereprocess.org > servicemanuals PDF This Owner's Guide describes every option and model variant available and therefore some of the items covered may not apply to your particular vehicle.
280 pages

2003 Ford Explorer Owner Manuals

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Find your Ford Owner Manual here. Print, read or download a PDF or browse a clickable online version. Access quick reference guides and more.

2003 Ford Explorer Sport Trac Owner Manuals

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Find your Ford Owner Manual here. Print, read or download a PDF or browse an easy, online, clickable version. Access quick reference guides, ...

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4WD not working on 2001 explorer sport

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2001 Sport Trac 4x4 does not engage.

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Disconnect one of your headlamps and use a multimeter to figure out the positive low beam and ground on the wiring, then using the ohm meter function check the high beam wiring back to the fuses and relays.
If I remember correctly, the fog lights are supposed to turn off when you turn on the high beams. So that switch system may need to be looked into on the controls.

Its not a relay, have your multi function switch checked out

low beam is a bulb on its own,usually under the big main bulb.the main big bulb works your normal night time driving and your high beam,ie.flashers.if 1 low beam has blown its more than likley a power serge blown the other side as they run off the same wiring.hope this helps.

sounds like the dimmer switch is going bad.

HAve you check fuses?

HAD A PROBLEM WITH ONE OF THESE EXPLORERS SAME TYPE OF DEAL I REPLACED THE HIGH LOW BEAM SWITCH ON THE COLUMN AND WHEN I DID SOME MORE INSPECTING I FOUND THE WIRE HARNESS WAS ALSO BAD THE PLUG WAS ALL MELTED.LUCKLY YOU CAN REPLACE THEHARNESS.MINE HAD NO HEADLIGHTS AT ALL,HOPEFULLY YOURS IS THE SWITCH OR LEVER.

The multi function switch does have the dimmer switch in it, but that is only a momentary contact to toggle the relay.
But is does not have to be the relay either, it could also be fuses, since the high beams and low beams have different fuses.
It is even possible both bulbs burned out at about the same time.
Use a test light to verify before replacing anything.

the element in your halogen bulb for high beam has blown, replace the bulb