As I mentioned in my original post, I did re-flow solder on the three connections that are reported to be troublesome. More recently I removed the solder, cleaned the surfaces up a bit and re-soldered. I think the connectivity is OK, and I think it was before as well. At 5x magnification things look pretty good "across the board" so to speak.

So I decided to try testing the individual relays (1 through 5, left to right, when opened module is laying flat on circuit board with relays facing you and fuses facing away). I simply used a common 9V battery which I connected to the two small vertical pins on the edge of each relay. Relays 1, 3, 4, and 5 all closed when I applied current to them. However, relay #2 (traction control) would not close when tested. Instead, relay #3 (engine control) would close even though my leads were touching the pins on relay #2. I'm thinking that the traction control relay is bad. Would that make sense, based on all the symptoms I described in my original post? Also, I've noticed that the horn (#1) and air pump (#5) copper coils are a little lighter in color than the middle three. Perhaps a sign of wear on the darker ones?