So, when I was looking at my engine diagrams for my 88 NA, I noticed that they all show a 'solenoid registor' located just under the air filter box. I have checked everywhere and found nothing on this. Any ideas?

 

Only used on early 1987 models. Your 88 is .........not early 87. It seems you have a wiring diagram for the early 86-87 1/2 cars. There's only minor differences b/t them and 88 models, and you found one of the minor diff.