Interesting, I thought it in some way triggered a relay for the antenna. Many years ago(2006) I had to mess with the whole dash wiring of my 99, and install a normal deck and only use the speaker wires(bypass the console and sub). I guess the antenna signal is compatible with any deck, but not a usable current.
BTW, the Lincolns of the 80's often had an antenna switch, which was more than a simple switch. That module might convert the antenna signal into a current. I have a Mark VII without that "switch", but it does have a module right behind where the switch went in past models.
I'd bet that module might do the exact thing the OP needs. It's about 2"x1x1.5" and I'd guess most early 90's Lincolns have it. The 91/92 Mark VII for sure does, and likely a similar model Continental might. In mine its located behind the trim that surrounds the radio, which is a flat part with several warning lights to the right. The module is at the far right, where the front of the trim shows nothing(the antenna switch used to go there). I don't have a picture handy or I'd post one.