04 Mustang GT Voltage/Electrical Issues

rlang

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Feb 6, 2020
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I'm new here but I needed some help so I figured this would be the right place for that.

My '04 recently hit 100k miles and I did some much needed maintenance on her in January mostly due to her giving me starting issues.

So I've replaced the spark plugs, battery, starter (that was a pain in the butt), serpentine belt, alternator, and the fuel pump and got a fuel system cleaning to boot. After all of that she was running like a dream.

But then several days later I noticed the battery light would light up intermittently but it didn't ever come on and stay on so I disregarded it (don't judge me). However, today as I was driving to work the radio cut off and the lights got dim and I realized the volts on the voltmeter were dropping. So I pulled over to the side of the road and watched the volts drop down to zero and I had no electrical power going to anything (no lights, blinkers, radio, etc.) and the engine was still on but the car wouldn't accelerate. After several moments of sitting there the volts on the meter went back up to normal and everything came back alive and the car was fine.

I intend to do an inspection of the battery cable wires and their connections on either side. But is there anything else that could be causing the problem?

Thanks in advance.
 
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the engine was still on but the car wouldn't accelerate. After several moments of sitting there the volts on the meter went back up to normal and everything came back alive and the car was fine.
Are you interested in a educated guess?

You have a bad or weak ground. Somewhere......

Howto perform charging system voltage drop test
 
Are you interested in a educated guess?

You have a bad or weak ground. Somewhere......

Howto perform charging system voltage drop test



Thanks for your reply.

What do you think the odds are that the alternator I got last month from Autozone is just faulty??

The bad or weak ground issue sounds a tad bit complicated to diagnose or find.
 
What do you think the odds are that the alternator I got last month from Autozone is just faulty??
Why guess? Test! Almost all auto parts stores will test alternator for free.

From the sound of it not even very basic voltage at battery tests have been done. What is the voltage at the battery with the motor running?
The bad or weak ground issue sounds a tad bit complicated to diagnose or find.
Don't discount the value of a good visual inspection. A good electrical connection is clean and tight. In short, it just plain looks right.

What is the status of:
  • The battery terminals?
  • The battery cables?
  • The large main B+ terminal?
  • The alternator's mounting points?
Have you done even a basic visual inspection?

Did you read the information in the links provided? If the voltage drop testing is understood and performed it WILL tell one way or the other IF an electrical connection is good or not. Bear in mind the value of information. For example knowing for certain that a electrical path is actually GOOD is important. It means that we know where the problem isn't.

Again my position on charging system is don't cut any corners. Nothing short of tip top operation should be accepted. With that in mind IMO you should start with a through visual inspection. Repair any problems found. Then have the alternator re-tested on the car. If problems still exist, start choosing choosing runs to perform a voltage drop test in big chunks. IE:
  • From battery negative to alternator case
  • from battery positive to alternator main B+
  • From battery positive the battery junction box (BJB) main terminal.
 
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