Truck battery discharge problem

[Klapatta]

Hey folks, maybe somebody can point me in the right direction with a problem we are having with my Son's 92 Chevy p/u. This truck has the 350 and is fully opted.
Something is causing the battery to slowly discharge all the way down after sitting for five days or so.
I have ruled out the battery as the culprit since we changed it over to second known good one and the same thing happened all over again, the first one is also less than 10 months old and took a slow charge back up to 13 volts just fine.
I have been told that a defective alternator rectifier bridge can cause this- the thing that I can't understand here though is that there no indication of any spark when one of the cables is touched to either battery post implying even a minimal power drain.
We disconnected the trailer brake control thinking that was the issue, but it was not. Everything electrical on it seems to work just fine.
I know of a guy at work with the same generation truck who tells of the exact same issue.
Has anyone heard of or gone thru this kind of crazy thing??
Any input is appreciated, this truck is too old to take to the dealer. Thanks!

[Jeff in Pa]

It won't fix the problem but what about using a trickle charger?
http://www.harborfreight.com/automatic- ... 42292.html

[ksanders]

Did you put anything at all new on it that was electrical? When I put a new radio in my truck, it would slowly drain the battery unless you detach the face. Oddest thing because it's now in my car and never drains the battery and the new truck radio wired identical doesn't drain it? Also, does it charge back up when you drive it from the alternator and good for another 5 day period of sitting?

[rweaver]

one of my buyers had the very thing it was the starter he went thru like 3 batterys before he found the problem

[mmzullo]

Ken,
Remove the neg battery cable. Get a 12 volt test light and put it in series with the battery and groung cable( hook 1 end to the battery and the probe to the cable). The light should NOT be on. If the light is on then yo have a draw. Pull 1 fuse at a time until the light goes out. Then figure out whats on that circuit. By the way make sure the dome light is not on when you test it. You have to keep the door pin switch in. If all things fail unplug the red wire off the back of the alt. The vg could be stuck on. If not do the starter test like Ray had said.
Good luck

[Klapatta]

Folks thanks for the input and comments, I appreciate it.
We started off with test Mike described using a .27 amp 12v bulb in series as a indicator on the ground side, it glowed yellow orange.
The first fuse to get removed was the dome light/radio memory supply. The door switch was overridden with a wood shim. The light went out.
The only device ever added on was the trailer brake control however that was long before the problem started, the radio is factory.
Is that normal for the clock to draw that much current? That seems like a lot to me

[l palma]

Ken,
Just a thought,is there a light under the hood??

[tompepper]

check that the glove box lite isn't staying on.

[mmzullo]

Radio memory or clocks should not show a draw unless the clock is a mechanical. If the light goes out with the removal of that fuse check to see if you have a delay box for the lights. Or a door panel light or someone had stated the glove box or hood light.

[Klapatta]

DUH!
After going through the wiring diagrams in the Haynes manual the radio memory circuit and courtesy lighting do in fact share the same 20 amp fuse.
I went out to take a look around a little in the dark at it and sat inside, took that fuse out about 3 times like that was going to fix things-yeah sure.
Then to what did my eyes appear?? Could that be a hint of light coming from the edges of the shut glove compartment door??
DUH! Moment of Clarity!!
By pushing on the door with about an ounce of force the light goes out.
He took the bulb out, dropped it too he did and now it's gone forever
Now ain't that just too bad
Thanks for the help everybody