Hey everyone thanks for taking time to help.
I have a 2000 Ford Mustang 3.8L V6 experiencing the following problem:

Here is the story, so yesterday after getting off work, I went to start my car. I get in, the dome lights cut on like usual, then put the key in the ignition and turn it, not to start but with gauges/radio/windows all working. Finally I turn the key to start and I hear one single click and everything dies. No dome light, no radio, no windows and simply removing the key and putting it back turns nothing on. Completely dead.
I figure its the battery died cause I accidentally left my cell charger connected. I unplug the charger, disconnect the battery and reconnect to check. Everything comes back on. I follow by trying again and the same scenario happens. One click then the death of my car.
I figure a jump might help overcome whatever the problem is. So I disconnect the battery, reconnect and with the help of a coworker and get the car a jump-start and everything is good. With the resetting of the battery after complete loss of electrical power and having a jumper-battery to help it starts.
I get home and turn the car off. Try to turn it on and dead.
While driving I did notice that an increased load, the a/c to be exact, dims my lights. But the radio with subs does not. Not noticeably at least. At really high, emphasis on really high, volume there is very very little flicker, almost unnoticeable.

Other information:
The battery is fully charged. DMM reads 12.78V.
When running after a jump-start the output is slightly higher at 12.98V
At 4000rpm the battery voltage reads 13.5V to 14V.
None of the wiring from the battery has been changed since original purchase date (father doesn't believe in replacing stuff like that) with the exception of the power wire to the BJB.

My Conclusion:
From what I gather I think the cause is the alternator. Maybe the power cables to the starter (Fuselinks maybe?) but definitely feeling like the output of the battery is too low when running.

Ideas? Thanks in advance everyone. If anyone has any other questions that would help get to a conclusion feel free to throw em out there.

 

You may be right with the alternator. I'd check for some kind of corrosion that could cause a slight short. I'm not too into all the wiring but that'd be a guess of mine.

 

I had a similar problem it ended up being the relay for my daytime running lights. If your running lights aren't coming on that's most likely what it could be.

 

Sounds like bad battery connections. Make sure your posts are nice and clean. And make sure the wires are not loose in the posts

Also just because a battery is at 12.6-8 volts doesnt mean its good. Thats not how you test a battery. All that means is you dont have a dead cell. You could have 12.6 volts with only 100 cranking amps and thats bad. Go to autozone or a likewize store and read the cranking amps of the battery.

 

If none of the other recommendations pan out, it could be the solenoid in the ignition switch. I had a similar problem with a crx. I would look at all the other suggestions first. They are far more likely.

 

Well the battery is new. Like three months old. The battery is a yellow top Optima D34/78. I think, not sure not at home, it has 770 cca. Ill post exact numbers later. The posts are definitely clean with no corrosion.

 

It isn't equipped with DRL. Also the problem started just yesterday if that helps.

 

You might have messed it up then.. Optimas are gel cells and have to be tricklecharged. Jumping them can fry them. Go get it tested. Side note. Optimas sit on the shelf for a while before sold. So its most likely older than you think. And also note they only have a 1 year warranty.

 

I googled the " jump start can fry your optima" and many others said they've done it with no consequences (multiple jumps). But thanks for the heads up I'll try to refrain from doing so.
If it is one year I'm sure it's from purchase because I doubt they'd hold me responsible for the fact autozone can't sell it. It was charged at autozone, the one I bought it from so if that's the case they can be held responsible for not being educated in regards to proper battery charging.

 

Did you get it tested?

 

Symptoms certainly sound like a bad battery or alternator. Have you been able to get it started at all?

If you can, check the voltage with it running, it should read between 13 and 14V. If its not then its your alternator.

If those check out, I would check your ignition system, there probably a short somewhere in there.

 

did you read

 

Looks like I missed that part. My sincerest apologies.

 

No I have not. However, my father and I figured it out.

Apparently the terminals were not conductive enough to allow the power to be drawn. For some unknown reason, they worked fine for almost six months and then just stopped.

Thanks for all the suggestions everyone, I greatly appreciate it!

 

Called it

 

I have a 1998 mustang 3.8 V6, was experiencing the exact same problem, same symptoms. Except my voltage meter was reading only slightly higher...
I spoke to all the "car guys" i know and was told its most likely a short "somewhere" so i got on google and started researching, And asked around at my local autoparts store and was told that it is most likely a short in the solenoid... So i purchased a rebuilt starter for like $100 and took it home. After two days of trying to get the old starter out (yes im new to working on cars) i finally got it done. I also cleaned off the terminals on the battery, and replaced the terminal connecters...
And that did it... She starts every time!!!
Hope this helps.