Hello there,
I recently bought a 1991 Si and I am having issues with the trunk. the latch on the trunk works perfectly, but the lock doesn't move when I put the key in. I'm not sure if the tumbler or core is jammed, or if I need to just mess with it a bunch. I already tried WD-40, and that didn't seem to do much.
Thanks for any help!

 

It could be keyed differently, but the more likely thing is that your key or part of the lock are worn. If it's your key you could try having the dealership cut you a brand new key based on your VIN (not a tracing of your current key). If it's the cylinder that's worn, you will either need to replace it or you may be able to disassemble it and fix it if you have some donor lock cylinders from a junk yard.

 

What DaX said happened exactly to me in my 90 Si hatch. Key would work everywhere but the trunk. Had the dealer cut one from the VIN and it worked perfectly from then on, and still does to this day after 10 years.

 

Sounds great! I'll head over to the dealership to get a new key. It does look pretty badly worn now that it's 30 years old