I've had this problem twice over the past year or so...................Park the car after a drive and the next morning the battery is so dead that it won't even turn on the courtesy lights. Here's what's happening and what's not: The alternator is charging properly at 14+ volts. The battery is fully charged when the car is parked Nothing is turned on inside the car, ignition is off, brake lights are off interior lights off. The battery checks out fine and charges up fully the next day with my taper charger to about 12.6 volts. When I recharge the battery and go to connect the positive cable, current jumps the gap until the cable is installed. So, I measure the current flow and see about 6.2 amps going out from the battery to something? So, I think maybe the ignition switch is on in the column and voltage is going to the coil but there isn't any volter at the coil positive terminal. So, the only other place the positive battery cable goes is to the starter and then the two fusible links, one to the lighting harness and the other to the firewall connector in inside to the fuse block BAT terminals. Before I go any further, is it possible that the starter has some kind of an intermittent short that's killing the battery when the motor is off? Like I mentioned, it's only happened twice in the last year or so. I do have the yellow wire hooked up at the starter which I don't need because I have run a solid 12 volt wire from the firewall to the coil to power my Dave Ray HEI distributor. Can that yellow wire that's still on the starter be part of the problem? Can the starter have an intermittent issue that only shows up once in a great while? I'm at a loss, guys. Throw me some ideas.
I had pretty much same issue after doing some tuning with my FAST air/fuel meter, which plugs into the cigarette lighter. Must have developed a short while screwing around with the crappy cigarette lighter power plug. I took a very small screwdriver and pried the terminals inside lighter housing free from touching anything and it quit discharging. Needless to say, I don't use the cigarette plug on the FAST unit anymore....that lighter is live all the time..
Hmmm. Occult electrical issues. My Favorite! You have already determined that there is at least sometimes a draw that should NOT be on when the car is off... If there is no juice at the coil, then it isn't in the run position. Perhaps it's still the ignition switch, but it's stuck in the accessory mode? Try the radio with the car off? Sorry for throwing out random thoughts. Do you have some non standard electrical, like a fuel pump or electric fan? I like the above shorted cigarette lighter idea too!
Leave the meter hooked up and start unplugging stuff. Start with the easy stuff like the alternator or horn relay. 6.2 amps is a massive draw. You should find it quick.
I've already unplugged the coil and the alternator and current still flows. Next time the problem returns I think I'll unplug the harness at the firewall to isolate the problem to either inside the car or in the engine bay. Problem is, now that I've started the car up after recharging the battery, the current draw is gone. That's why I was thinking it might be something in the starter. At least until I find the problem, I'm gonna have to unplug the battery while the car is parked at home.
Good thought but, I've changed to an internally regulated alternator and the factory regulator is still there but, unplugged.
Sure, that's how I found the 6.2 amp draw. I've also eliminated the alternator, coil, and regulator. The next step is to isolate whether the draw in inside or under-hood. I wanted to do everything possible before starting to pull those glass fuses as they often break. I posted on the forum to see if anyone has had a similar problem. I was thinking that the starter might have an intermittent "high resistance" short.
The Trunk lamp Theory is nice too! There aren't that many things that are hot when the ignition switch is off. Definitely check the Cig lighter outlet. The intermittency of it makes me think of a stuck relay...
Your local hardware store should have replacement fuses for a few bucks. It'll be worth risking breaking them to help diagnose. Nothing is plugged into the lighter socket right? My century's socket is always on it's wired pretty much from battery->fuse box-lighter
Think....What was the very last thing you messed with the day it started acting up? That's how I found the lighter as the culprit with mine. I yanked all those glass fuses,etc... Nodda. Even broke one.
It sounds like your car is stock with nothing added . Is that true ?? Follow Larry's advice and eliminate each circuit one be one by pulling the fuses . You could also check the Alternator by unplugging it . Alternators can drain the battery internally . Especially the internally regulated ones that you say you have .
