Between the battery and the vacuum Reservoir, can anybody help me out?

 

My truck has an oxygen sensor plugged in there (3 total in that truck), but I have EEC-V in a 96' 351W.

 

Mine is an obd2 F350 with a 460ci engine. I have 3 HEGO's as well. The 2 in each header plug in above the transmission. The one that plugs in downstream has wiring coming off the back of the transmission.

But I do notice that it is the aqua green color of the O2 sensor plugs.

 

Its capped so it could be un-used or a test port. Is there writing on the cap?

 

Just a part number. I'm curious what it's for. Like I said, its got that aqua/teal color. And on my truck, only emissions plugs have that.

 

It is C1003. Used for the HO2S on some trucks but not used on your truck.
The power wire in it is powered by the PCM power relay (361 R) on some trucks and by a fuse on other trucks. The plug also has sensor ground wire (359 GY/R) and may also have the computer 74 and 387 for HO2S sensor and power control wires.

 

The EEC-V system is pretty flexible to tune, is it possible to use this to plug in another sensor to use for a wideband?

 

I have no idea. The C1003 plug appears in several configuration in the 1996 wiring diagrams.
As I noted above it may be powered by a fuse or the PCM Power relay. The will be a ground wire in it and more than likely two other wires that end someplace before getting to the PCM Computer. There is not much information on a not used plug.