Explorer loses all electrical power

[sd_iconoclast]

I have a '91 Explorer EB 4x4 4.0.
The other day I was coming down my long steep driveway at night. Suddenly, the engine died, as happens frequently when I am idling downhill.
I tried to restart the engine, and all power went out in the vehicle. All lights went out outside and inside the car. The only light left on was the check engine light. I had to coast down the driveway in darkness with no power brakes or power steering.
When I looked under the hood, I heard several relays clicking on and off every few seconds. I found that it was actually the EEC power relay that was clicking on and off, and all other clicking relays had power coming through it.
After a couple hours of work with my digital multimeter, I narrowed the problem down to 1 wire. It is the wire from Fuse 10 in the power distribution box to the ignition switch. See attached diagram.With fuse 10 pulled and the ignition switch connector unplugged, I see 12 volts at the fuse end of the wire and 1.5 volts at the ignition switch end. According to my Chiltons schematic, this should be a yellow wire that is now totally isolated, So I should see 0 volts. On the car, I see this wire as green at the fuse end and yellow at the ign switch end. Clearly my schematic is wrong. Does anyone have a better schematic?
Oh, I guess I cannot post attachments so the diagram will have to wait

 

[Anime]

If the alternator is original and the mileage is high (200,000+) then it's likely the brushes in the alternator are worn past their useable state and you should probably have it rebuilt or buy a new one.

It could also be a wiring issue, or even something directly related to the PCM, since those are known to go when the capacitors they contain leak onto the circuit board and cause all sorts of electrical problems, including random shutdowns and no-start situations.

Check all the fuses, check all the relays (especially the fuel pump and EEC relay) and swap them out with known good ones to double check. If nothing else works try a new battery, new alternator, and pull the ECM to take off the cover and see what shape the caps and board are in.

 

[sd_iconoclast]

Thanks, Anime.
However, I have actually already eliminated all those items. I have narrowed it down to the one wire. I was just hoping somebody had the schematic from factory manual. The Chilton's schematic is simplified (it does not show comnnectors for one thing).

 

[tweakedlogic]

Check your power cables and ground cables for corrosion. that's what mine was.

 

[sd_iconoclast]

Check your power cables and ground cables for corrosion. that's what mine was.

Dear Mr. TweakedLogic. I guess you have not been at this very long because you do not seem to understand the proper way to approach these problems. A veteran working on old cars (such as myself) knows that you do NOT start by looking at the easiest, most common explanations for problems like this. Instead one must disect wire looms, remove the dashboard, order factory manuals, and trace multiple circuits with the Digital multimeter before checking battery terminals. It is best to follow this procedure while youer wife is complaining that the car is unrelaible and your friends tell you what an idiot you are for buying a 20 year old car.
I hope you have learned your lesson.

But seriously, thanks. It was the negative battery terminal. I wish I would have taken your advice more seriously when you posted it

 

[malohnes]

Dear Mr. TweakedLogic. I guess you have not been at this very long because you do not seem to understand the proper way to approach these problems. A veteran working on old cars (such as myself) knows that you do NOT start by looking at the easiest, most common explanations for problems like this. Instead one must disect wire looms, remove the dashboard, order factory manuals, and trace multiple circuits with the Digital multimeter before checking battery terminals. It is best to follow this procedure while youer wife is complaining that the car is unrelaible and your friends tell you what an idiot you are for buying a 20 year old car.
I hope you have learned your lesson.

But seriously, thanks. It was the negative battery terminal. I wish I would have taken your advice more seriously when you posted it

Haha...made me laugh. Been there done that!