I just bought a 99 Explorer v8 2wd to replace my aging aerostar and to tow my boat. I already knew it had this problem and a destroyed rear diff when I bought it, I figured this would be the easiest problem with just a new switch. I was wrong.

pulled the fuze
pulled the headlight switch
pulled the relays at: power dist. box, keyless entery/alarm?, the box under the dash
disconnected the harness from the GEM behind the dash and from the keyless entery/alarm

lights only go out when I pull the park lamp relay

I know what you may be thinking. But no. Its still not gonna be that easy.
The relay is not bad or being activated. Its just acting as a jumper from pin 4 to 3. So out comes the test light.

At the park lamp relay (without the relay in)on the relay module I get power at 1, 5, and 4. When I ground 2 with the test light, the headlight relay kickes on. Which seems normal to me by my assumption of how the system works. Which is that these relays are only for the RAP module to flash the lights by grounding the 2 pin. Anyway...

I think I've narrowed it down.

According to the wiring diagrams, the 4 pin should only get power from the headlight switch and the GEM from a white/black stripe wire. With the relay in (only to jump the power)I have unpluged both the headlight switch and GEM, and the lights stay on and there is power at 4. I figured the white/black wire may have a short to 12v and I would just bypass it. Then today I can disconnect the battery, then reconnect it and the lights will stay off. Keep in mind all other relays are out and everything is unplugged. If I plug the headlight switch back in, cycle the switch, the lights will go on and off correctly, but will eventualy stay on. Even after removing the head light switch.

Does the white/black wire go to anything other than the switch, GEM, or relay.

It doesn't say so in the diagram but I can't figure out why its getting power intermittently. Still thinking it could be a short I did a wiggle test on the dash harness to try to get them to come on if off or off if on. Nothing. Driving me nuts! Any help or advise greatly appreciated.

 

My diagram shows a white/violet wire as the ground for the relay(it may look black by now).

The anti-theft system activates(grounds) this wire like you mentioned, and the autolamps sensor grounds this wire. Do you have autolamps?

They also show this wire going to a "dimmer relay", though I believe this is just a common point with the parking light relay ground/activate wire. I can't figure out though why anti-theft, and autolamp circuits would activate a dimmer relay.

 

To answer your question, no. I don't have autolamps. I did however find the partial cause to my problem. I was gonna just replace the white/black wire from the switch to the relay to the GEM. Even though it really bothers me not to find the cause of the short.

A little about me, I am a classic Ford mechanic. I don't really work on anything after 1973. Anyway.

I knew that there maybe other shorts that I don't know about yet. So I figured I would narrow it down further by cutting one of the white/black wires from the relay module to the GEM. I unmounted the module to get to the backside a found some melty wires. The white/black, tan/white, and red/black wires melted together. I pulled the wires apart and taped them up. Yeah right if you thought that was gonna fix it. So I cut the white/black wire from the relay module to the GEM. I tested for 12v at the GEM and switch and found the wire from the switch still had 12v. Dug a little deeper and found melty wires behind the switch as well. The white/black, blue/orange, and another wire I can't remember. Feelin pretty boned right now cause I know I have to go through the harness and do 2 things: trace out and find all the damaged wires and repair them, and find the cause of the overheated wire.

Wait! Just thought of something. Tomorrow I'm gonna remove all the fuses and reinstall them only one at a time and see whats gonna give 12v to the white/black wire at the headlight switch. Now that I think of it, the ABS kicks on everytime I hit the brakes and the ABS light is lit in the dash. Suppose this is realated? Are there any common wires that overheat? Thanks.

 

The tan/white wire is known to overheat going to the headlight switch. It's a common thing to happen on the trucks, but I do not know if it's common on the explorers.

Whatever caused it, you now have a serious problem(I think you already know that). When they bundle these wires together, and some of them melt, it damages totally unrelated circuits that are bundled together, and makes it very hard to troubleshoot. I think you should label and pull the complete harness out and and look it over. You may only have to take part of the harness out if you find it only melted certain sections. I know it sounds bad, but I think you are going to have gremlins in this vehicle until you repair/re-insulate the damaged areas.

Here's some places in California that have used harnesses for sale.

1999
Dash Wiring Harness
Ford Explorer WIRING HARNESS-GOOD AS-IS 102 $250 Costa Mesa Auto Dismantlers USA-CA(Costa-Mesa) Request_Quote 1-877-300-1894 / 1-949-548-7013 Request_Insurance_Quote
1999
Engine Harness Wiring
Ford Explorer 5.0L AWD, CHECK PART # W/DEALER 101211 $225 All Trucks Parts USA-CA(Rancho-Cordova) Request_Quote 916-638-3500 / 877-770-8782 Request_Insurance_Quote
1999
Engine Harness Wiring
Ford Explorer hd27366 4.0 auto ac hd2736 $224 Truck Parts Company USA-CA(Baldwin-Park) Request_Quote 1-800-411-8718 (Cali only) 626-337-7264 Request_Insurance_Quote
1999
Wiring Harness Loom
Ford Explorer 4.0L 2WD-AUTO ENGINE - LOOM- 24359 $200 Globe Used Auto Parts USA-CA(Pacoima) E-mail 1-818-890-0305
1999
Engine Harness Wiring
Ford Explorer 4x 4.0 elec shift jc041290 jc0412 $189 Truck Parts Company USA-CA(Baldwin-Park) Request_Quote 1-800-411-8718 (Cali only) 626-337-7264 Request_Insurance_Quote
1999
Dash Wiring Harness
Ford Explorer 4.0 auot 4x elect jc041291 jc0412 $174 Truck Parts Company USA-CA(Baldwin-Park) Request_Quote 1-800-411-8718 (Cali only) 626-337-7264 Request_Insurance_Quote
1999
Headlamp Wiring Harness
Ford Explorer A 3E3546 $150 Waterford Truck Dismantling USA-CA(Waterford) E-mail 1-800-544-3488
1999
Dash Wiring Harness
Ford Explorer 5.0L AWD, WALK IN ONLY 101211 $150 All Trucks Parts USA-CA(Rancho-Cordova) Request_Quote 916-638-3500 / 877-770-8782 Request_Insurance_Quote
1999
Engine Harness Wiring
Ford Explorer 4.0L, 4X2, ENGINE HARNESS, W/FUSE $135 All Trucks Parts USA-CA(Rancho-Cordova) Request_Quote 916-638-3500 / 877-770-8782 Request_Insurance_Quote
1999
Engine Harness Wiring
Ford Explorer 4.0 SOHC INJECTOR LOOM ONLY HD07632 HD0763 $120 Truck Parts Company USA-CA(Baldwin-Park) Request_Quote 1-800-411-8718 (Cali only) 626-337-7264 Request_Insurance_Quote
1999
Engine Harness Wiring
Ford Explorer A62555 $120 US Auto Salvage USA-CA(Indio) Request_Quote 1-760-347-7700 Request_Insurance_Quote
1999
Dash Wiring Harness
Ford Explorer A62555 $120 US Auto Salvage USA-CA(Indio) Request_Quote 1-760-347-7700 Request_Insurance_Quote
1999
Headlamp Wiring Harness
Ford Explorer A62555 $75 US Auto Salvage USA-CA(Indio) Request_Quote 1-760-347-7700 Request_Insurance_Quote