OK guys, I don't even know where to begin searching previous threads so, I'm just throwing this out there. Sorry for the length.
2002 Explorer Sport Trac, 4.0L, 5-Speed Manual, 247k miles.
A couple of weeks ago, while driving home, the electricals started fading. Lights dimmed, wipers slowed down, power windows moved very slowly, AC died. I turned off everything I cold and limped it home. I charged the battery overnight, suspecting a bad alternator.
The next day, I took it to AutoZone to have it tested and was told battery and alternator were both good. However, the tech didn't seem very knowledgeable. So, I went to Advance Auto and had it tested again. This time I get good battery, bad alternator, which is what I was expecting. Bought a new alternator and installed it. All good for two weeks.
This morning, I get it and put the key in the ignition, dash lights up as usual but when I go to start, I get a brief crank and then nothing. Dash goes black, power locks won't work, remote won't lock or unlock the doors.
I'm thinking battery is now gone due to the previous alternator issue but when I hook up the charger, I get a green light, no blinking, which indicates a full charge.
Herre's where it gets weird...I put a small jump box on it, still no joy. Just for informational purposes, I disconnected the negative terminal, waited 30 seconds, reconnected it, put the jump box back on, and boom, starts right up and runs normal.
I took the battery to Wal-Mart (where I bought it) and had it tested out of the vehicle and it tests good.
At this point, if I try to start it, I get the same, dead electrical system after a brief crank. Put the jump box on it and nothing BUT, disconnect the batter for a few seconds and then jump it and all is good.
Wires are all good, connections solid and no corrosion that I can see.

Any thoughts? Starter relay? Ignition switch or relay? I even considered a bad alarm system. The truck didn't have keyless remote or alarm when I bought it so I had the Code Alarm system added later. I thought maybe the "kill" circuit was malfunctioning.

Any ideas are appreciated.
I've gone through about htree cycles of this so far today in getting to work

 

Are the battery cables both clean and tight? Are they original style cables with molded ends, or have the cables ends been replaced with those temporary bolt-on style ends? When you use the jump box are you clamping onto the battery cable ends or elsewhere?

-Rod

 

Cable ends are clean and tight. When I replaced the battery last November, I cleaned everything up, used felt spacers on the battery posts under the terminals and coated with anti-corrosive spray.

Rechecked everything I could easily reach yesterday. I'm clamping the jump box onto the cable ends, directly above the battery posts.

Since my post yesterday, it's started fine three times in a row now.

Tomorrow I'm going to chase the cables all the way back and recheck all the grounds I can find.

 

Are the cable ends the original molded style or have them been replaced with the bolt-on temporary style? The temporary cable ends do have a bad history of allowing the copper to corrode under the clamp and make poor connections.



-Rod

 

Looking and guessing will not see resistance and internal corrosion,, perform a voltage drop test .. lets get some raw data ..