emofacing

i have an 87 NA w/210,000 miles. all three systems stopped working at diff times. before i pull the cpu, has anyone else had these systems fail and if so, what was the cause? i have the wiring diagram and i'm going to go through it to check for shorts, bad connections, cpu problems. just wondering if anyone has already had and fixed this issue or if anyone has an idea about the cause other than what i already plan on going through. it's going to be fun. =)