ABS test plug?

ok so i searched for the answer with no luck. car is 95. theres a plug that says "anti lock test" right next to the coolant overflow/ intercooler pipe on driver side and the harness that plugs into that was just hanging (not plugged in). pretty sure i got the car like that. What does that do and are you supposed to keep it plugged in or not?

on that note, does anyone have just the plastic connector with an intact clip for that they want to sell. my retaining clip is broken off and it just pops out.

That is the Anti-Lock Test Connector used to catch the codes from the ABS System when using a code reader.

Not sure I understand what is plugged or not plugged into what from your description. There should be a cover over a connector that is shaped similar to the EEC/PCM Test Connector with wire connections made into the connector. It (the Anti-Lock Test Connector) does not plug into another connector just to the cover.