Tracking a Possible Electrical Short

[TXNSTANG]

My '05 GT all of the sudden started dying on me the other week. The dash lights, radio, and electronics would flash off and on and then completely die and the battery would be completely dead, in fact, my battery was fried.

I pulled the alternator to test it and found where the cable from the battery to the back of the alternator was completely fried.

I put a new battery and alternator in, but it wouldn't start after installation. We were gone on vacation for two weeks so I figured the battery was drained. When I put the charger on it, it immediately went into fault mode. I even tried another charger and it did the same.

When I pulled the positive cable off the battery, the charger started working and charged the battery.

It's obviously an issue with a short somewhere! Anyone have any suggestions on where to start looking? I will probably replace the cable between the battery and alternator, although I don't know if that is the culprit or not

 

[bambam 06]

You are probably going to replace the battery cable harness, p/n 5R3Z-14300-BB.

 

[brasil]

..check the NEGATIVE side of your harness. I had the same issue with my Alfa Romeo.. the negative cable was "internally broken ".. engine died..not energy at all..
THe reason for the short is simple.. while the negative cable is out of oder.. the positive cable tries to close the circuit . So I installed a new negative (battery to ground ) cable..
Problem fixed.

 

[TXNSTANG]

Ok, so here is an update: I replaced the alternator (and battery) not long after my original post back in August. I also replaced the alternator and noticed the cable was completely fried at the back of the alternator. I ordered the wiring harness bambam 06 suggested. I didn't realize that the harness didn't have the cable from the battery to the alternator. I ended up getting an alternator wire from my local parts store as none of them carried the OEM. I did discover the terminal post is a bit larger than the hole on the wire connector, but I was able to drill it out a bit. Also, the Ford OEM cable has a dog leg on it to help route it properly.

Everything was going fine and working up until today (October 19), then I had a repeat of the original problem. The alternator spontaneously stopped charging, and the car was running strictly off the battery until it died. Later this week, I'll pull the alternator to see what went out on it. I'm also going to spend the money and get an alternator cable w/fuse from PA Performance. I might as well and order the alternator connector with the pigtails. I did notice it appears there may be a crimp in one of them. Maybe it is not telling the computer the right voltage? Guess we will see! It's only money, right!?! LOL

 

[DieHarder]

Need to check major grounds first. Then perform a voltage check across the battery with a VOM with the engine running. Should be at least 14.2 vdc. If not do a voltage drop test (neg lead on passenger strut tower ground; pos lead on the body of the alternator). If you're reading voltage your grounds need work.

Since you replaced the battery harness I'd say you might want to add an extra ground from a mounting bolt at the alternator and run the other end to the ground at the passenger strut tower. This will ensure the ground at the alternator is the same as the body ground. Once you get done recheck running voltage across the battery (should be 14.5 vdc or better) and the voltage drop test (0v vdc). You can get the hardware (4 ga cable; eyes) at HD/Lowes or most any hardware store.

For more info see: Finally found the cause of my low voltage - Beware the all important grounds.

 

[TXNSTANG]

I finally got a weekend off to put the replacement alternator in. I used the PA Performance fused cable and ran a ground from the alternator mounting bolt to the strut tower. I also replaced the PCM connector at the alternator. There was a pinch point in the wires, so I cut them and replaced the connector.

I even pulled the after market radio to check for any type of shorts. I did find a loose hot wire that ran to an old amp the previous owner had. It doesn't look like it had been shorting out, but I took care of that issue.

It is running at 14.5 volts right now, but so was the other one.

I mean, the last two alternators literally fried, which in turn ruined the battery because the car was running off it before it overheated and ruined the cells. Crossing my fingers this does the trick

 

[TXNSTANG]

So I've been running the replacement alternator for about a month now. My son drove it the other week and when he got home, he stated the check engine light was on. I ran a diagnostic, and it is showing a P0622 code (Generator Field "F" Control Circuit Malfunction). I'm really hoping this is not the PCM. Grrr....

 

[TXNSTANG]

So, it is throwing the P0622 code again. The alternator still seems to be charging. I've replaced the connector to the PCM at the alternator as I did find a crimped wire. I ran a ground from the alternator to the body (strut tower) to ensure it was properly grounded. I'm at a loss now.

 

[TXNSTANG]

I ended up taking my 'stang to a local mechanic. As mentioned above, the alternator is charging and everything "seems" to be working properly (according to them). I asked if they used an oscilloscope to check the PCM wire at the alternator to see if it was fluctuating like it should be doing. They told me that "it was reading voltage just fine", which really didn't answer my question. I guess I will have to by a multimeter with an oscilloscope and check it myself. Outside of that, I cannot find anything that would be throwing the code and screwing up the charging system!

Do I bite the bullet and just get another PCM? I hate throwing money out the window like that, but I'm about at wits' end.

 

[JC SSP]

Consider checking the SJB located on the passenger side foot well and check for corrosion.

 

[86GT351]

Look very carefully at the smart junction box for water intrusion

 

[TXNSTANG]

Thanks! That'll be my next step.

 

[86GT351]

Thanks! That'll be my next step.

Also check the underhood cowl drains and remove the rubber inserts.