Where does this short (5-6 inch) wire go?

[032vstang]

Does this look like a ground? 2003 mustang GT. Replaced intake and now reverse lights,speedo, and blower motor is out. Could this have something to do with it? The wire is only about 5-6 inches long and literally nowhere to plug up. Any ideas?

 

[mostsmooth]

Does this look like a ground? 2003 mustang GT. Replaced intake and now reverse lights,speedo, and blower motor is out. Could this have something to do with it? The wire is only about 5-6 inches long and literally nowhere to plug up. Any ideas?

I'm no expert, but it doesn't seem like they would design a ground wire like that.
If you want a random guess,it reminds me of the oil pressure sensor wire on my 95gt

 

[n0v8or]

Clips to a threaded stud located near the fuel rail (red arrow in attached photo). I doubt if this is the cause of your electrical issues. If the manifold was replaced without disconnecting the battery, one or more blown fuses are a more likely cause.

 

[n0v8or]

After further thought, I withdraw my blown fuse theory . I was searching for a single cause of all your malfunctions, but now I think there are 2 separate causes.
Regarding the heater mode selector, the dashed yellow line in the attached image is the vacuum hose for the heater/AC damper position actuators. It passes through the firewall on the passenger side just below the refrigerant lines. This 1/8" hose should eventually connect to the plenum, just after the throttle plate, where shown by the yellow arrow. I suspect this vacuum became disconnected during the intake swap.
As to the reverse lamps, speedometer, and odometer issues, a potential common cause is the transmission harness. The reverse lamp switch and output shaft speed sensor are mounted on the transmission (I do not know where, because I have an automatic). If the connector for this harness is disconnected, it can cause all of the 3 malfunctions you mentioned.