Hello, I have changed the tail light panels and still get water from rain. The trunk leaks and it runs into the back seat floor on the passenger side.
Wondering if one just needs to change the seal around the trunk??
Thank You in advance for your thoughts!!

 

It is probably the light fixture itself that's leaking. Is this what you mean by "panels"? If those are good then the seals are suspect, the rubber foam ones between the lights and the body. The seal around the trunk usually doesn't leak unless there is super heavy water flow that flows up and over the lip. All this is providing you don't have some body seem letting water in somewhere...

 

What year and make do you have? Does the car have a sunroof?

 

I'm assuming we're talking about a 240 sedan here...

its a bit of a poor design... the lip around the trunk opening is fine, it keeps the water out even when the seal is in poor shape, but the water from the roof gutters drains down around the trunk opening directly onto the top of the tail lights.

my experience is, even relatively new 240 sedan tail lights will end up filling up with water in heavy rains, then that water leaks out the inside of the lamp fixture into the trunk...

I've been known to drill small drain holes at the lower corners of each light 'box' on those so the water drains out the back.

now, you DID replace the foam seals when you installed these new tail lights? aftermarket lights don't always fit quite right, and sometimes you end up needing to use a bit of aquarium sealer (clear silicone RTV/Silastic/whatever) around the light assembly where it joins the body...

now, the other thing that can happen, unrelated, there's some drain hoses in the trunk on each side, one goes to the air vent tray thats at the base of the rear window, and the other goes up the C pillar to the sunroof (if you have one). these can plug up, and when they do, water can overflow into the car. there's another set of drain lines on a sunroof car that go down the A pillars, these aren't visible or accessible anywheres, when they plug up with debris, water will dribble down onto the front floor, also splash down around the sunroof inside opening.