I found the 6 pin diagnostic connector just fine, but I cannot find the 1 pin connector anywhere. Did the 88 F250 (351w) use a 2 pin or other type of connector instead of a 1 pin? There are several disconnected 2 pin connectors around this.
From the picture in the haynes manual and here Ford Fuel Injection How To Run a Self-Test

show the 1 pin to come out of the same harness as the 6 pin diagnostic connector, yet there is no plug on mine, or even signs that there was.

Any ideas???

 

maybe youre looking at the abs test connector

 

The EEC test harnes is over behind the washer/coolant resovoirs on the older trucks..

 

Yup, exactly where I am looking. Part of the problem is this wiring harness has been spliced in several places. I cant tell if it was because something chewed the wires or if someone just spliced in. It is entirely possible the connector just isnt there, but I cant even find bare wires where it should be.

I fixed the problem that was throwing the CEL, but I would like to find it for the next time.

 

You're probably going to have to trace the wire from the EEC connector considering the condition of your wiring harness, STI is pin 48 on all trucks. You can safely remove the connector as long as you disconnect the battery first. When you do this you'll loose anything stored in memory so it won't do you any good this time but you'll have it for future issues.