HEGO orange wire grounds to manifold??

I was searching through past posts on this site for info. on HEGO trouble codes 41 & 91...I came across several posts that mentioned an orange wire in the engine compartment that is supposed to a ground wire (not sure why it would be orange?) for the O2 sensors. This turned on a light bulb in my head...because when I rebuilt my motor I had this 14 gauge orange wire coming out of the 10-pin connector's wiring harness right behind the upper manifold & T/B area...by the firewall of the engine compartment. At the time I had know idea what the wire was for...I didn't remember removing from anywhere when I pulled my stock motor out...so I just left it there hanging with the end wrapped in electrical tape. I've been driving my car for years now since the new motor and never thought anything about it. I only recently have been trying to tackle the codes that my EEC-IV is spitting out...because the performance of my upgrades seem to be up to par...except my mph could maybe be a little higher in the 1320' on motor. So do any of you know what orange wire I'm talking about? Or could one of you with an '89-'93 Mustang take a look at the wiring harness coming from the 10-pin connectors for an orange wire? Is it connected onto your manifold somewhere? I'd really appreciate a confirmation here. I'm pretty sure this wire should in fact be grounded to the manifold...but I wanted to make sure before I go and drive it. Don't want to melt something ya know?!