This is a pretty common problem with c. 1990 Civics (and
other Honda models?). It's a do-it-yourself job and does not
take too much time. You need to dis-assemble the rear
taillight assemblies and either (1) buy and install new
gaskets; or (2) clean off the old ones and apply temperature
appropriate silicone (sp.) caulking to both sides, then
re-assemble.

I did the second back in 2003 for my 1991 Honda Civic. No
leakage since, and my car has driven through some serious
downpours.

For genuine Honda gaskets and manuals with info on
dis-assembly, see the links at
http://home.earthlink.net/~honda.lioness/id9.html . But I
did not need a manual to figure out how to get the
taillights apart.

piperspost@webtv.net wrote in news:26677-44E50011-96@storefull-
3337.bay.webtv.net:

This happened to me on my 94 Integra,and it was a small plastic piece on
the brake pedal lever that had crumbed and fell off.It is supposed to push
on the brake light switch when the pedal is not being pushed,thus,if it's
missing,the switch thinks your foot is on the pedal and the brake lights
stay on. The part was only about $6,but it's not easy to access,so I had
the dealer do it,total about $50.