i have a 1988 bird that i am putting the dash back in i have three connectors that look like stereo connectors but the stereo only has two ports any idea where the other one plugs in at
Possibly for equalizer option would be my guess
It could also be the premium sound plug in.That most of the time does mean a factory EQ in these 88 models. I just remember when installing an aftermarket radio with the premium sound needing to locate the secondary non premium speaker plug. That sounds like what you have found.
Hope that give more insight
Stuckman