Excessive Parasitic Current Draw

[chuck d.]

I'm trying to repair a problem on my elderly fathers 99 Suburban 1500 SLT with the 5.7 Lt gasoline engine. Even with a new battery after it sits for several days the battery is drained to where it will not operate the starting motor. The alternator puts out a good 14 plus volts when the engine runs. I installed an accurate ammeter in series with the battery and something is drawing around 900 milliamps (0.9 amps) when the vehicle is parked. Obviously this is way more than it should be (50 milliamps or less). I have disconnected the alternator in the event of a shorted diode in it. No change. In the dark I've looked for any light that is on. Nothing. I've disconnected both the glove box light and the light under the hood. I have indivually pulled every fuse, relay and circuit breaker in the flat fuse box by the master cylinder in the engine compartment and every fuse in the interior fuse panel in the end of the dash. The only fuse that stops the current draw when pulled is a 50 amp fuse in the engine compartment fuse box labeled 'BATT' . It is between a 50 amp fuse labeled 'LIGHTING' and a 40 amp fuse labeled 'IGN A'.

I'm wondering if anyone has a good electrical schematic for this vehicle and can tell me what this 'BATT' fuse powers and therefore what could possibly be causing the excessive current draw.