Interesting. That points to damp wiring.

More symptoms of defective wiring.

You must determine if the TCM thinks it has a problem. Find the module and
watch the lamp in the window. Note the number of flashes, if any, when you
turn the ignition on. On my old Prelude the module is under the carpet where
a passenger's left foot would rest. Pull back the carpet to see the
indicator.

It's likely that the TCM is sensing some moisture-related problem under the
hood. The number of lamp flashes indicates the location.

I had almost exactly the same problem (91 Accord), except the gear indicator
showed the selected gear, and my 'S' light was on. (Actually, the 'S' light
would wink out sometimes, and the car would drive normally. Then, it would
come on, and the transmission would go into 3rd gear.) It seemed to be
related to wet weather.

Here are some links that may help - or not :)
http://www.hondacarforum.com/honda-3/16786-flashing-s-light-91-accord-lx.html
http://www.honda-tech.com/zerothread?id=962851&postid=33094332 (old, some
pictures gone)

After reading some advice on the Internet, I came to the conclusion that the
TCU was bad. Some of the literature suggested it was worth a try to fix the
board itself. So I removed the TCU and exposed the board. Sure enough, there
was a bad capacitor, as evidenced by some obvious leakage onto the circuit
board. I bought a replacement at Radio Shack for $1.50, unsoldered the old
capacitor, cleaned the board as best I could, and soldered the new
replacement in. That did the trick, and that repair has held for about 5
months now.

If you feel adventuresome, I suggest you remove the TCU and look at the
circuit board. If you find an obviously bad component, try replacing it.
(Leaky capacitors are one thing - you can still see the specs on the side;
burnt resistors may totally obscure what they were, as you cannot see the
colored bands.) Chances are, you have not much to lose, since a rebuilt TCU
will probably cost about $150.00.

-- R Flowers

Thank you to everyone who replied with advice!  As an update, I
replaced the TCM, and the car is running smoothly - in wet and dry
weather!

Thank you to everyone who replied with advice!  As an update, I
replaced the TCM, and the car has been running smoothly - in wet and
dry weather!