unfortunatly, this is where my help has to stop
not because I don't want to, but because it happened about 6 years ago, and I don't remember exactly what I had to do.... to tell you the truth, I can't remember if I unplugged the latch closed switch, or actually physically adjusted either the latch on the trunk lid or the bar on the back of the trunk
maybe you could look at the latch system and see if there is any adjustment that can be made???
other then that, you will probably have to get some info from someone that owns one of the 87 - 91 cars.
I am glad to see that it helped you out, I was kind of going out on a limb with that one, but good to see it worked out.