Is this a CD player/headunit?
Go to walmart buy the Scosche Toyota wiring harness for that year and then a installation kit for the toyota. Wire the Pioneer wiring harness into the scosche harness (will be about 11 wires). Assemble the installation kit, mount the new headunit in it. Remove the old headunit. Plug the scoshe wiring connector into the stock connector you pulled out of the back of the stock hu. Plug everything in DONT FORGET THE ANTENNA! then slide the new headunit it and you're done. If the car has a power antenna make sure you hook up the remote turn on wire. This is kind of a vague description give me a call if you need anything matt I will be farting around the shop tearing the 87 apart all night. The wiring kit and install kit should run you about $15 max at walmart.
EDIT I looked it up, that headunit is Double DIN so you won't need the mounting kit (installation kit) you will only need the wiring kit. Wiring is $6.95, or like $11 at autozone.
[This message has been edited by Mr.PBody (edited 02-08-2008).]