2002 Mustang GT auto

Confirm if the engine continues to run or has to be restarted.

Suggest starting with the easy stuff first. Check the battery. It is clean? Are the terminals clean and tight?

Don't cut a corner here. Today's cars will not run without a strong battery.

Check the grounds. Has any work been done esp around the radio?

Inspect the connections to the alternator. Recommend having the alternator tested at your local autoparts store. Have the tester look for excessive AC ripple.

Based on the results, we can go from there.

Bad alternator?

akozlowski06 said:

The engine does NOT need to be restarted after this happens. Have had a test run at autozone when the problem first started. Bought the car used a couple months ago. The battery is fine the alternator is fine acc. to the autozone people. Have had it tested with the battery light ON. Cables are clean, posts are clean and the cables attached well. The battery gauge on the dash says that the battery is fine in addition to the check at autozone. The only thing that they did tell me though is that its pulling extra amps on starting. The radio was checked all the wiring is fine. But what I did notice about the electrical in the car so far is that the trunk button, dome light switches and my power moon roof all do not work.

Click to expand...

What do the dome light and trunk release have in common? Answer - the Generic electronic module (GEM). The GEM shares the same ground as the cluster and the radio. The ground is located left side of the center console.

Coincidence?

Have you checked all of the fuses in the Battery Junction Box (BJB) and the Centeral Junction Box (CJB)? Esp fuses F2.20 and F2.25 in the CJB.

I wouldn't trust the dash voltage meter at all. It lacks the fine resolution to display anything of value. I have personally had alternators go out (confirmed bad) and the dash voltage meter still showing good voltage.

I have much more faith in the operation of the battery charge warning light.

Note, since this is actually affecting the running motor, my gut tells me that this is a bad battery or alternator. I know what you are thinking, "how can this be a bad battery? The car is running.". Today cars need the battery to provide excitation for the alternator field coil. If the battey drops out, the alternator will shut down when there is a load change.

The days of jump starting a car with a totally dead battery are OVER.

It is entirely possible there is a defect in the battery that is allowing it to "open". Vibration could be making it come and go. My advice, don't assume that just because the parts store tester says that your battery is good, that it still couldn't have a problem.

FWIIW, the battey light coming on is a symptom that should not be ignored. I have reviewed the wiring diagrams and I do not believe a missing cluster ground could cause a false battery charge warning. The battery warning circuit is simple and well designed. So until proved otherwise, I think it is a valid symptom.

IMO, a "blinking battery light" is more likely to be related to the alternator. An "open" in the battery is most likely to present as a "sudden" electrical failure that would almost certainly kill the engine.

Check the ground strap from the left hand motor mounts to the frame rail.

Does your car have under drive pulleys and the battery light blinking at idle? Does your car have a really BIG sound system? If no, IMO the evidence points to a bad/weak alternator.

Remember that bad grounds or loose cables can also cause the reported symptom.

How old is the battery and where are you located? A hotter climate will kill a battery a little bit faster than a seasonal area. Also, is there any custom audio equipment? Had a similar issue after I put a sub in the car, with similar results.

Also, if the terminals are not super tight the car may be cutting out due to disconnection of the ground terminal, had this happen as well with a blinking battery and abs lights. I would replace terminals and battery (unless they both are less than a year old.) as that cannot hurt anything, it is maintenance of our cars regardless.

Inspect the small connector to the alternator. Is it clean? Are there any bent pins? Is the connector push in all the way? Does it appear to be snug and making good connection.

Check fuse F2.5 in the CJB.

What is the voltage at the battery when the car is off? When the motor is running and the light is off? On? We really need to confirm the alternators output to decide the next pinpoint test to run. Post the results.