Starter circuit problem

My 1988 Honda Accord LX has 330,000 miles. It runs like a top when it starts, but it hasn't started in several months. I thought it was related to the cold weather. It mysteriously started again a few weeks ago, only to disappoint me again the following day. The starter motor isn't getting any juice.

The battery is good. The starter has been tested. I'm guessing the ignition switch works, because I hear some relay clicking near the main fuse box under the hood when the key is turned to start.

That fuse box is some sort of engine control unit as well, right? Can it be tested outside the vehicle? Is there another part of the starter circuit I should check?