I have a 1999 Ford Explorer and the auto headlight feature ceased to function. I think a relay is shot but don’t know which relay is for what. How can I identify the propler auto headlamp relay?


Don’t jump to conclusions. It may not be the relay. There is a photocell somewhere that senses daylight and there may be some solid-state control circuitry, unless it uses the main ECM. Those items could be malfunctioning. Anyway, get a Haynes or Chilton’s repair manual at any auto parts store.


If the headlights still work manually, then it’s not the relay.


As Stevef mentioned there is a photocell in the rearview mirror.

It gets dark, the photocell sends a ground to the park lamp relay & to the low beam relay. The relays close & the lights turn on

BTW, the same relays are used to flash the lights when you use your keyless remote. Do the lights flash when you lock/unlock with the remote?

The relays are not used in manual mode.

The above is how it works according my “1997 Explorer electrical & vacuum troubleshooting manual”

Odds are your 99 works the same.

The relays are behind the center section of the dash.

BTW. the EVTM manual that I mentioned is worth 10 times the 35 bucks that I paid for it at


I bet your Exploder has a lighting control module (LCM) in the dash. If so, it controls all the lights, the rear window defroster and maybe more. There are a bunch of relays on its boards. It is not an inexpensive component. I would be looking at other things anyway. The photocell, as mentioned above, wiring faults and the autolamp control are all likely.

You can get a wiring diagram by subscribing to Your local library might subscribe to this or another database or have paper repair manuals.


Much changed between 1997 and 1999 with Fords. The relays are in the LCM (on newer models it’s called the FEM). If the lights work at all, it’s not the relay. It could still be something else with the LCM. Or, it could be with the light sensor. The light sensor is on the dash behind the same plastic piece that the red LED blinks in for the electronic key system warning. The photo cells in the mirror (if you have that option) are only used for the auto dim feature of the mirror. There is one pointing forward and one pointing rearward. If there is more light in the rear one than the front one, the mirror dims.


Thanks for the heads up guys. I’m surprised that this 99 is wired so differently as compared to my 97.

I think I prefer the electrical system on my 87 Ranger.

Number of fuse boxes & fuses on my 87: 1 & 18

Number of fuse boxes & fuses on my 97 Explorer: 2 & 55.

“Aint progress grand”

I think i’ll hang onto my 87 for another 240,000 miles.