Is the light coming from the inside of the slide floor where the carpeting meets the wall? I had a crack the full length of the 8 ft. slide where the flooring meets the side walls. Turns out I had a leak in the far left side of the slide, probably from a bad seal. The slide floor had rotted badly in the front left corner and had dropped enough so that the side wall separated from the floor. The way it is attached in the factory is really bad with a piece of aluminum angle attached to the slide frame with light weight 1" screws screwed into the side wall of the slide.
The fix was a new floor for about $3,000 with the 8' x 1" slide floor being shipped from Indianapolis to Florida, plus labor at my local RV shop, which would require the slide to be removed to repair. I opted to make repairs myself by cutting out the rotted section and securing a new piece of pressure treated 3/4 inch plywood sandwiched with a piece of 1/4 inch luan to get my 1" floor replacement piece. I screwed it through the bottom of the side wall, as was the old floor and bridged the old floor with a stainless steel plate, that was also sandwiched between the new floor piece and the side wall. I thru bolted a new piece of angle to the floor and frame of the slide and thru bolted the exterior wall to the angle. The screw heads were hidden on the exterior by a trim piece that attaches the bottom trim piece. I plastic coated the underside so it would move in and out smoothly and so far it is holding up. I could jump up and down on the plate covered new piece with no movement. Needless to say I had all the slide seals replaced and was due to re-carpet the interior of the slide anyway. The cost was minimal and a couple days of sweat equity. I was unaware of the leak inside and the TT is 8 years old.
Inspect the underside of your slide to ensure there is no rot or signs of leaks and check how the slide seals extended and retracted and the condition of the side & top seals. My slide was also slightly out of adjustment with the rotted end not completely sealing to the trailer when fully closed. Really poor construction, but from what I hear this is common with most brands. Hopefully yours is something different, but check seals, slide closure adjustment and any signs of leaks, i.e. water stains or mold. Good Luck!
2008 Modified Surveyor 303
2010 Dodge Ram Laramie 4x4
2013 From FL to Pick up Surveyor Islip,LI, PA,NY,VT,NH,MA,CT,NY and Home
2014 Sebastian Charleston,SC to Finger Lakes, Lake Erie, Lake Cowanesque,PA and home
2015 Sebastian to PA,NY,WI,MN,return to NY and home
2016 GA,SC,NC,TN,KY,OH,PA,NY,to Sebastian,FL