ignition switch/ alternator/electrical question

I had a dead battery yesterday morning and wanted to find out why it went flat.

My battery holds 12.42 volts after a charge and is only a year old so I doubt its the problem. With the car at idle im only getting 12.6-13.3 volts which seems very low. also with the lights on other accessories my voltage dips as low as 12.2 volts. When I hold it at 2500rpm i only get around 13.3 volts.

When I back probe the alternator wiring harness all 3 wires have the same voltage as the battery, including the lug terminal on the back......is that normal?

Starting to think the alternator is bad. what do you guys think.

I put in a weak battery from a project car(it had a hard time turning over) and went for a drive and noticed that my speedo was jumping up to 30kmph when i was stopped. after letting the car rest for about an hour I came back out to start and barley had enough juice to get it started, it ran fine but when I got home the battery was dead(clicking sound from the solenoid)

Later that day after charging the new(ish) battery for my tbird I went to a friends house a few miles away. This time I disconnected my battery when i arrived. After a few hours it still had a full charge and drove. After sitting overnight my batt is still at 12.42v. Im starting to think there might be something draining the battery when the park is off. Also when driing home last night my drivers side signal indicator in the gauge cluster stayed illuminated and the blinkers on that side do not work. The Passenger side works fine. Combined with the jumping speedo does that sound like an ignition switch problem?

Sorry for the long post, any input would be greatly appreciated.

Joe

edit.

today my alternator is putting out 13.8v at idle and climbs with the rpm, blinkers and gauges work just fine too. I'm going to replace the ignition switch anyhow i hear its responsible for all sorts of bizzare electrical issues.

I've heard that a bad alternator can cause strange things also, like jumping tach and speedo. Might want to get it tested.

Check condition of batt terminals and major grounds (engine to frame, batt neg to frame, batt neg to engine, etc).

I've seen the issue Pete said, and the alternator was replaced and I've also done what Jeff said also. Also ran an extra ground for peice of mind. Never had issues after the grounds were known to be good. You can always take them apart and wire brush/sand paper the connections put them back together and paint them to keep from corrosion.

Thanks for the replys

sometime this week I'll go get my alternator checked out. No biggie if it is bad, been wanting to to a 130amp upgrade anyhow.

I noticed driving today that the issue with my blinkers only happen when the headlights are on. they do not blink when the blinker switch is pushed all the way down and and locked but i can make them flash by manually moving the switch then releasing it and repeating. ( hope that makes sense to anyone who is reading) I think there is a short in the wires from the headlights or blinkers....I'll post after i have some time to work on it later this week

Im also going to run a few chassis ground and a new one to the block. Can I run em directly from the negative terminal?

The factory stock alternators sucked, and they were just barely sufficient for the accessory loads these cars could produce stock. If you have any intention of upgrading lighting, stereo, etc. than I strongly suggest upgrading to a 3G and never looking back.... I got a 160 amp from RJM Injection Tech with a plug and play alternator harness and a bunch of 2ga cable to make new charge and ground cables for a fair price considering the gains in reliability I will see out of it.

Had some time to look it the car today. Turns out that the ground wire(the one that goes to the rad support)had an internal brake in it. Fixed that and ran a few new chassis grounds while I was at it. Everything works great again.

thanks for the help.