Battery drain issue

[Alloyvert]

Working through a wide range of gremlins on my '64 C10 and the overnight battery drain issue is driving me nuts. I realize there are a ton of threads on this topic, just looking for some reassurance I am on the right track.

This truck sat since '98 before I acquired it recently and had a wide range of "interesting" electrical hack work done including the use of a ton of wire nuts. Thus far, I have installed the following new electrical parts: both under hood harnesses (starter/distributor & alternator/main cab feed), voltage regulator, horn relay, alternator, battery, and battery cables. And in the the cab, new light switch and heater switch. I also redid/replaced the main ground straps (chassis to fender, cab to chassis, motor to firewall). The charging circuit seems to be working normal as I am measuring 14.2 volts while the truck is running and the truck remains running with the battery disconnected.

My first overnight test on Sunday was disconnecting the drivers side engine harness from the firewall and the battery voltage was unchanged overnight. Next step was attaching a test light in series with the positive battery cable and with everything connected, it was lit. So I started disconnecting just about everything in the dash starting with the ignition switch, then each fuse and wire from the fuse block with no change as the test light stayed lit.

Could this be something in the fuse box itself? It does look very crusty, but seems odd that nothing changed with everything disconnected. I recently ordered a new dash harness from Classic that includes the fuse box, so that is next on the swap list.

Open to any other ideas or feedback. Thanks!