plug behind glove box?

[LtSmellMy]

I have a 1987 chevy 1/2 ton tbi 305 that I swap an older rebuit 350 and 4 speed in. I removed the factory tbi unit, wiring and computer because i'm gonna get a fitech throttle body. but i was wondering what this plug is? The plug was hooked up to the wiring harness for the ecm or ecu and runs to the driver side of the dash. Any ideas?

 

[1987 GMC Jimmy]

That looks like the ALDL (Assembly Line Data Link) connector. It's hard to make out the pins on that connector, though. If so, that's where you probe your codes, test your fuel pump, test your AIR pump if equipped, get serial data to look at live engine data, and test to see if your lockup solenoid is working.