I have a '90 s5 T2 Vert (ex japan)
Ever since I replaced the drivers side Seatbelt I cant get the Trunk Light to go off, I have spent hours checking circiuts but cant find the cause.

I have checked the switch on the bootcatch and it works fine, the circuit that the switch is on is closed even without the swith plugged in, I have both the Haynes and Factory service manual and can't find a curcuit Diagram to cover the trunk light.
Does anyone have any bright Ideas?

 

At the latch in the trunk you will find a light blue w/ green stripe and a black. You will need to remove the back (tail light side) of the trunk liner plastic to get to the wire.

The blue/green should only have ground on it when the lid is open. If you slide a screwdriver down the slot where the latch goes you can see how the switch and latch works.

It is not uncommon to have the trunk seals get old and if they are leaking to get water into the switch (and trunk).

 

Happened to my 88 vert- kept draining the damn battery. Bad switch. I found a new trunk latch assembly somebody was clearing out on ebay w/ a new switch.

Did the trick.