Anyone have any idea what this is? A small antenna mounted inside, top drivers side. Antenna is pointing down. 1994 S10 ZR2.

 

Welcome to the forum. Your truck could have had a remote start unit or aftermarket alarm at some point in it's life.

 

Definitely something aftermarket. I'd recommend seeing if you can find a brand name, model number, anything you can on it and the do a search on the web. Odds are there is something else hiding under the dash and/or engine bay.

 

I have something like that on my 2001 blazer passenger side rear quarter window. The antenna cable goes down into the rear storage over the passenger wheel where & is connected to some sort of equipment. No clue what that is either. LOL
It also has a factory antenna as well & removing the one on the rear quarter glass has no affect on my radio reception.

 

There's one on my truck and it's a "Shark" remote start system. All of the associated wiring and control boxes are usually mounted just under the dash by the steering wheel and fuse box as this is the easiest access point for all of the ignition controls and things like that.