I have a 98 Accord V6. The battery keeps dieing overnight. We have tracked the problem to the #12 position Fuse in the Fuse box under the hood. It is labeled Accessory and Backup. Does anyone know what is run by this fuse?

 

That might lead a person to think the accessory socket and back up for radio, clock, and ECU.
The amp draw across that fuse should make a test light glow dimly.

 

There is also an accessory in both inside fuse boxes. What is an ECU? I had a car starter hooked up a few years ago. I am wondering if it could be powered through fuse #12 under the hood. I have shut off the toggle switch fo rthe car starter and found my car battery still dead in the am. My Neighbor tracked the power drain to the #12 under the hood. I am assuming the accessory socket and radio are the fuses labeled accessory in the inside fuse box.

 

Engine control unit. Honda officially calls it a PCM = Powertrain Control Module. It's the combined engine/fuelinjection computer combined with the transmission control computer.