Rachel wrote:
> The following ONLY occurs during wet weather:

Interesting. That points to damp wiring.

> I noticed that with the engine running and while at a
> stop, if I shift into other gears, the D4 light on the dashboard
> remains lit (i.e., if I shift to reverse, the R light and D4 light are
> lit).

More symptoms of defective wiring.

> I think the Transmission Control Module (TCM) is bad, but I wanted to
> get others' opinions. Is there a way I can test if the TCM is bad?

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.

--
Chuck