Repair is being performed for the owner - a little old lady that's been 'handled' on this for a while... The vehicle is a Ford Ranger - '92 - 4.0. I picked this forum cuz there's more posters and it's a generic problem, methinks...New battery, new cables, - I got in at this point... Hooked up Christie - Alt is charging perfectly. When engine is shut off, state of charge steadily declines from 100+% to 75% in about 1/2 hour. Steady similar decline overnight leaves battery completely zero. Removed alt for bench test on Car Quest equipment ... says All tests good... Any ideas on where to start looking would be appreciated. I can see no spark when hooking up neg battery cable... though I occasionally hear a relay (?) clicking below the fuse box... otherwise, nothing seems to be on - lights, etc... even so, it's a pretty heavy drain - I'd think I should "see" something when I attach the cable...You can shoot me an answer direct if you have any ideas... Thanks!
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I remember a guy that a had a battery draining problem due to a bad fog light install by one of the previous owners. Does the truck have any aftermarket electrical stuff?

If the battery is draining itself while parked then you've most likely got something thats PULLING that charge, it can't just go nowhere. If you want to make sure the battery is good then you can get it load tested at the parts store. You can also remove the battery and measure the voltage across the posts OUTSIDE of the truck (should be around 12 volts, give or take a few volts), then measure it again in the morning and see if it's different. This will help isolate the problem.

Welcome to the forum! I'm gonna move your thread to the right section. Right now it's in the F-Series trucks section

Most parts store alt testing equipment will only test if it is charging or not. They wont show if the regulator is sticking. The right way to test for a draw, is to install a parasitic draw test adapter (most marine sales stores have them as battery disconnects). Test drive, working all bells and whistles, then hook up an ammeter for DC amps. Hook up one lead on the battery cable end, and the other lead on the battery post. Then turn the disconnect switch on the adapter. That will give you a reading of how much amp drain there is. Generally, .025 is acceptable. Newer vehicles need up to 1/2 hour for the modules to fully power down before you can get an accurate reading. When you have a steady reading, start pulling fuses until the drain disappears. When you find it, look toward whatever is on that fuse circuit.

Remove the negative battery cable and connect a test light between the negative battery post, and the negative battery cable. Now start removing fuses one at a time until you see the test light dim. When it does, you have found the circuit that is drawing the current. Then go from there.....

Good luck!!

Bob is dead on on how to find the drain on the battery.