Sorry,I didnt see this earlier. I did that very same thing once. You need to change out the dash harness along with the engine bay harness to run the 88 SMEC electronics in your 87. Its easier than it sounds as the rest of the body harness is plug and play with both 87 and 88 dash harnesses. If both cars have the same color dash just swap the dsah completely so you dont have to pull all the dash wiring off the one and put it on the other. Good luck...no one know what is envolved? or if it is possible?
Oh ya,thats right. Its been like 5 years since I did that so I totally forgot. I was switching interior colors so thats why I went with the dash swap way. You also have to cut out the hole in the firewall to fit the round plug for the SMEC harness as the 87 haas a square hole.The wiper motor plug is different.