Troubleshooting '85 Carrera

[BlueTone]

Hi all, had a strange, possibly unrelated series of events that caused a dead battery and stuttering of the motor in my '85 Carrera. Here is a summary of events.
Riding to Hershey yesterday, 119 miles from the home base, listening to some tunes via iPod interface (thru a 2 channel amp and powered sub). 30 miles away, wife needs to charge her Blackberry, we have the USB cable so we plug that into the Kenwood USB port. It charges the phone and as soon as we get said 30 miles away from Hershey, the car begins to stutter throughout the rpm range. Not enough to stall us, it idled fine, but as soon as rpm's were raised, it began coughing. Then the radio lost all power. I checked the powered sub and there was still a light on, indicating it was still receiving power. We stumbled into the Hershey parking lot and walked away. Little did I remember the strip of I78 where they ask you to turn on headlights because it was a work area. I left the headlights on for approximately 30 minutes. Over the loudspeaker they announced a 914 that left its headlights on and that jogged my memory. Went back to the car and turned the headlights off and walked away. The battery is less than a month old so I figured it was ok. We get ready to leave, get in the car and we have a dead battery. Go to get a jump (yeah, that was me they announced that needed a jump). Jumped the car off, started right up, Kenwood head unit restored to initial startup menu (as if power had been disconnected) and the car drove flawlessy on the way home. Now I'm trying to figure out what is going on. Was it coincidence that the radio lost all power while driving while the car exhibited either fuel delivery problems or electrical problems? Did leaving the lights on for 30 minutes really drain the new battery? Or was the battery loosing charge while I was driving it, causing the radio to lose power? Did charging a Blackberry thru the USB port have anything to do with it? When Will of Precision Motorsports changed the battery, he tested the alternator and it was fine (again, about a month ago). The car is going back to Will this week for regular service, I would like to have an idea of what happened yesterday so maybe we can figure out what to do. Any ideas?
Thanks
Ric

[steely]

Glad you made it home alright - I wonder if the ground condition could have played a role, as if the assumed good alternator would not me able to charge the assumed good battery. Even though you had a healthy load, I would have thought the alternator would have kept up (w the sub, headlights and USB charger). But it sounds like the voltage may have dropped below some threshold that the head unit needs.

I don't know if the stumbling is a symptom, am sure someone will.
I suggest he check the charging system/gnd strap etc.

[ant7]

hi,
if you have a sub connected to your head unit it could be that, when these things go faulty, they can drag a lot of current, once the head unit lost power the sub unit got switched off, hence the battery re-charged.
Either way, i hope you get to the bottom of it, let us know.
Anthony.

[mackskibum]

BTDT. Take a hard look at your voltage regulator, and possible install a volt meter- at least temporarily. My guess is that either the alternator or VR are getting weak, or the stereo is drawing more than the alternator can supply. Whatever you do, find the culprit- if you get to 16-18v from the VR, it can get expensive- ask how I know...

[gregwils]

Agreed. I had my motor out and forgot to reconnect the yellow wire to the starter. The car was not being properly charged and was running on battery power. As it got near the end of the battery charge - started bucking as it was loosing power. Sounds very similar.