Hey, so I'm looking in the engine bay for the Tach sensor wire. Can't find it but I found these, and idea?

 

The top photo is the self-test plug and single wire plug is the STI wire.
You ground the STI wire to start the self-test.
Self-Test Input (STI): A dedicated circuit used to initiate the PCM Self-Test.

 

How do I do that? Lol

 

The bottom photo is the holder for the EEC Power Relay, Fuel Pump Relay and the self-test plugs.

 

Not sure on a 7.3 IDI so I will let someone else answer that question.

 

you don't . the engine has no electronics to test.
not sure if the trans will give test codes through the plugs, i never messed with the E4OD.
the tach sensor is on the front of the engine, screwed into the top of the timing cover next to the oil fill.

 

if you ever see the over drive light flashing (you'll get hard shifts too at the same time) then you'll plug in an obd 1 code scanner there to get your codes from the E4OD transmission.