Really the only way to narrow down a draw in a vehicle is to set up a volt/amp meter at the battery and start pulling fuses one by one... pain in the butt considering where the fuse panel is on C3's.... however, even thouhg you put in a new alternator, you might want to have it checked for a bad diode... been there done that.. only took 3 days to drain a battery... and also (my own doings)  the two wires going to the alternator, i accidently got them reversed(the original plastic connector got brittle and broke, so i just got them individually plugged in..... again, took only 3-4 days and dead battery.  Otherwise, i'd have to concur with the consensus(there, i used my 'big word' for the day) and just get a disconnect switch.. :)

We discovered quite accidentally this weekend while doing some underhood cleaning on my brother's 72 that the idle solenoid was warm to the touch even tho the car had not been run in two weeks.  Indeed it was energized while the ignition switch was off.  Later we discovered that the battery had run down.  I charged it for hours and it still tested weak.  We swapped in a spare battery and drove it some.  Afterwards, the idle solenoid was NOT energized when the ignition was turned off.  We have not yet begun to research or diagnose, but perhaps our discovery will provide a clue for someone or perhaps someone has seen this before and has a clue for us.

Looks like a lot of you guys use a battery disconnect. Where is a good place to put the disconnect switch in a C3 vette? Close to the battery would be best I imagine but inside the batterybox would be difficult to reach every time I want to drive or stop. Maybe behind the seat in the riser panel? Where do other members have it located?

I have a battery disconnect switch that is attached to a side post battery terminal.  It has a small wheel that you turn to connect or disconnect the battery.  Really convenient inside the battery box.  You can find them by doing a search on Corvette Central or any of our other sponsors.  Only cost about 10 bucks or so.

Mine is the same as Larry's.

The slow drain is normally found to be the alarm system, or the natural draw on the mechanical clock...neither one is really worth the effort to track down, imho. The later('77>) cars will sometimes have an issue with the courtesy light timer, as well.
It's just a good idea to install the disconnect on them...safer than having a surprise short somewhere setting the car on fire.
I disconnect mine anytime I am not in the car...period. A little paranoid, perhaps, but still...

On top of being a fail-safe against a melt down, it works pretty well at keeping it from being stolen...most thieves ain't smart enough to look for the battery behind the seat. If they were, they prolly wouldn't be thieves to start with.

I am having the same problem with my "77', my battery will drain in about 3-4 hours.  I've found that if i take my + cable off and reconnect i can hear a click, lastnight i took my center console apart and found two modules in front of the gear shift which is where the clicking was coming from, I have not figured out what the modules are yet because i have only owned the car for a week.  I will stay in touch, will be tearing into it this weekend.  Some of the other readings on this site say that "sharks eat batteries"

OOPS!  I was looking at this post to refer to it, and accidentally added to it.  If a moderator wants to remove my stupidity, I would appreciate it.

Larry
VetteSpecialties2008-06-06 10:39:41

here is a  check for batterry drain problems

The culprit in mine was the underhood courtesy light.