Some Electrical Guidance Please...

I was going to post this as a continuation to my recent major thread, But thought I might get some fresh perspectives if I started anew.

So here's the update. Got my car back from it's major a few weeks ago and all was well. Very well in fact. Approximately four days afterward however, I started experiencing the dreaded dash lights and then no power syndrome. I initially believed that my alternator had gone out again (three times in the past 14 months already) and FASTCARS forwarded me some new parts with which to rebuild said alternator. But before doing so, we (FASTCARS mechanics and I) communicated by phone as to the symptoms and varying voltage readings.

Here's what I'm experiencing right now. Car has 12V constant when measured at the battery and the rear power bar. When the car is started, I get 13-14.5V at both locations as well. If left to idle, the voltage begins to drop back to the 11.5-12V range and remains there until the fans kick in to high speed, at which time the voltage goes up into the 13.5 range. When I turn on the recently repaired AC system however, the voltage goes back down to 11 or so and then begins to plummet. Turning it off again doesn't reverse the trend.

The consensus is that the alternator may not be at fault, but I probably have an open short or weak ground somewhere. I have load tested the battery and found it to be fine and am now searching for various ground points throughout the car. The one from the frame to the transaxle is secure as is the one from the alternator to the pan. Can anyone point me to the other grounding sites, or better yet show up at my house and free me from this,"Groundhog Day"-like experience? Seriously, a little F-Chat guidance is all I seek (unless Ernie and the Stooges want to take a road trip). I appreciate the help I'm receiving from Craig and Francisco at FASTCARS as well.

Sorry for the long narrative guys. Thanks for any suggestions, Henry

 

Saturday the 21st at Vince's. Just leave the AC off for the ride. You can do that. You're healthy. You'll survive. We may be able to fix your car. Or mess it up worse. Or get you trashed so you don't care.
Seriously, if it happens when you turn on the AC, start there. Maybe a bad AC clutch. Does the AC work?

 

Does it only happen when the car is warmed up? On one of my other cars, I had an issue where the voltage would only drop off when it was warm. It ended up being a weak connection between the +12V terminal on the alternator to the battery. It was fine until it heated up. I replaced the connectors and that resolved the issue. I have also seen someone else on here with a similar issue that had to replace the other wires that go to the alternator.

 

It sounds like it is could also be the voltage regulator. Works cold but dies once heated. That is internal to the alternator so it needs to come out if that is the case.

How old is the battery? ...and is it an Optima?

 

Henry.. you could ride up with me to Stoogie day on 09/21 and get some pointers if you don't trust driving your F355 all that way. Call or e-mail if you'd like to join me.

 

Thanks for the pointers/offers guys. Bruce and Vas, I'd love to meet up with you guys on Saturday but I have a funeral to attend (and I don't trust the car to make the drive anyway). The AC wasn't on when the car stopped last time so I'm not sure that's the culprit. I had a new wire/plug installed from the alternator. I assume it's the one that runs to the battery.The battery is just over one year old and is an Interstate 34A (I believe).

I had it load tested and it came out fine, but have reason to believe that it may not be taking a full charge. After more testing this afternoon, I got a 14.3V reading at the power bar in the rear immediately after starting her up. After the fans cycled through and I turned on the AC, wipers and high beams, the output went down to 11.75V and pretty much remained there. Revving the engine didn't increase the output, leading me to believe that the alternator isn't responding accordingly. I drove it around the block a few times with no dash lights or issues. By that time the car had been running for half an hour. I recently found the wiper/brake light fuse burned out (any connection?). Going to have the battery tested again tomorrow.

Thanks again guys...

Henry