Haynes Paper Repair Manual 1997 Ford Explorer
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 onBTW, 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. 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. Mionet world edition review.
2014 Ford Explorer Service Manual Pdf
2010 Ford Explorer Repair Manual
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.