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I am dealing with a similar issue on a 2000 Taurus SE.
# 1 - car will shut off while driving and restart in 3-4 seconds by itself then run ok. Sometimes is will completely shut down. I got stranded on the side of the freeway for 20 minutes until it decided to start working again. I noticed the ABS
light on the dash was on very dim, no other dash lights were on while the car was off.

# 2 - When turning the ignition key to the run position, the ABS light will be on very dim, no other dash lights are on , no radio, etc. car will not start. I turn the key off, and nothing happens. If I leave the key in the run position within 10-60 minutes it may decide to just suddenly come back to life electrically. At that point I can either have a successfull start or it will go back to "Electrical Failure mode" as soon as I turn the key to start position.

So far I have done the following with no fix yet:
- Checked with Ford dealer to make sure the formentioned recall for brake light has been complied with. It has.
- replaced the ignition switch
- cleaned and ohms checked the 5 engine bay grounds
- swapped PCM relay out with A/C relay
- split engine bay harness plug and inspected pins and recepticles for damage or corrosion. No defects.
- pulled and checked all relays and fuses in all three electrical panels (2 near the battery in engine bay and 1 under dash)
- with the electrical system in "failure mode" I did a detailed shake and grab of all accessible electrical harnesses under the hood and dash. No effect noted.
- the only thing that can quickly reset the issue is to disconnect the negative battery cable and touch it to the positive cable for 15 seconds. Then reconnecting it the vehicle comes back to life. It may start and run for up to an hour or a couple minutes, or will just go back into "failure mode" as soon as I turn the key to start position.


Battery and charging system checked out ok, I checked for loose connections under the dash, none.
This happens in all weather conditions.
Any ideas what this could be?
 

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Just checked voltages at ignition switch. Definitely an issue here. 2.5-3.0 VDC and when I demand current for any additional systems like press the brake pedal for brake lights, turn on headlight switch or turn key to start position this low voltage quickly drops to zero.

While I was taking these readings I heard a subtle click and my voltage increased to 6 VDC. I was still able to bleed it off to zero by turning on headlights and such. Then after a minute or so the electrical in the car came back online and the meter read 11.49 VDC at ignition switch and I wasn't manipulating anything. Then I turned key to start position from run having the 11.49 VDC and everything went to zero again to build back to 2-5-3.0 VDC again. So odd, I am looking for some better wiring diagrams than I have access to on alldatadiy.com to help me trace these wires to the source of there power. Any wiring diagram resources and additional information and guidance is greatly appreciated. Thanks for getting me to look at this issue at the ignition switch, I agree we are on track. I read over the issue you faced and the new wire you had to run. We will see if that is what it comes to for this vehicle.
 

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That bundle in the fender has screwed a few of us. Hit me with a PM if you need more direct help with it
 

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So here is what I have found so far with the limited amount of time I have lately to work on this electrical issue.

The ignition switch receives power from a LIGHT GREEN/VIOLET wire. It begins its life from the battery junction box 40 AMP fuse F107. Then goes down the line to a splice that provides power to the starter relay pin 87, the output pin 30 of that relay I presume goes on down to the starter solenoid. From the splice we continue on through the left fender through the firewall to a connector C264 pin 34. Resistance checks between connector C264 pin 34 and fuse F107 are @ 12.4 ohms. A bit too high. I will dig into this more tomorrow.
 

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Rec'd PM. I am at the Red Sox rolling rally and don't currently have access to my diagrams. If you can ask a specific question I will try to provide help. If you need specific diagram assistance try a PM to member Thesavo.
 

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I think I resolved issue

The solution was to replace the battery ground cable. The odd thing is that a regular resistance check with a meter looks great, but once the high amperage demand of the starter trying to crank is attempted only 1 VDC would pass through the cable.

Battery positive post to fender ground was 1.0 VDC
Battery positive post to battery negative post was 12.49 VDC

No obvious sign of corrosion at either end of the cable with just a general look. There was however a small amount of surface corrosion under some heat shrink wrap that was covering the crimp of the battery terminal connector. I can only guess that the issue was within that crimp. Thank you for your help. I hope that this will help others if they stumble upon a similar issue in the future.
 

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In the firewall on the passenger side. Look for a very large loom of wires going into a rectangular connector with a bolt going through the center.
Firewall is in the back. Fuse box is in the front no where close to the firewall
 
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