I've noticed that my 90 hatchback had some water coming into the trunk with it pooling at the bottom by the spare wheel. It's got the wooden board wet and a bit of mold on the carpet. I poored water all over the back but can't see where its coming in but think its coming in underneath the carpet by the rear lights.

So any ideas how to seal or water proof the trunk? I was already planning to by a black rubber trunk mat to lay over the carpet but if the water is coming in underneath, I'll obviously need something else.

 

Are you sure it's not leaking from the weather stripping that runs along the roof?

 

I don't believe so, I've seen no evidence of water coming in from above and when I poured water all over the rear, again saw nothing. I noticed that there is a gap though between the body and the tail lights although this looks to be by design so I think maybe water is getting in there but then not sure why it's feeding into the trunk if it's meant to drain through this gap.

 

Tail light seals can shrink and start leaking. I'd check there.

 

Water leaks in EF civic

My 89 has the exact same water leak. After a good rain I’ve put my hand back there behind the plastic near the tail light and felt water droplets. Is that wood cover thing OEM? Mines fucked...

 

Is it a car with a sunroof? The sunroof drains terminate right behind the taillights and can become clogged.

 

this is exactly what I assumed it was

 

I've noticed moisture inside the taillights so I'm assuming this may be my problem although I'm still a little unsure which part the 'gasket' actually is on the tail light

 

There is a large foam/rubber gasket that fits over the back of the tail light and is compressed against the car when you tighten everything down. Most of them are fairly brittle after 30ish years and may need finessed to get even a marginal seal. I would suggest removing both tail lights, drying and cleaning the contact areas as much as possible. When reinstalling snug all the fasteners, then slowly tighten in a pattern like with head bolts or wheel lugs so you don't crush part of the gasket and leave another area too loose.

Edit: Part #4 in this diagram: https://www.hondapartsnow.com/parts-...taillight.html