Chris is right, that is the MAP sensor which measures manifold vacuum. My Regina manual gives the following voltage vs. vacuum figures:

14.5 psi..........4.4v
11.6 psi..........3.2v
8.7 psi...........2.1v
5.8 psi...........1.1v
2.9 psi...........0.5v

There should be 5v coming in at terminal C. Ground at A. Varying voltage at B. If you have errors stored by the computer, there should be an fault code set if the output is too high or too low. My manual shows the use of a "connector box" which connects between the sensor and its connector. Terminals on this box allow you to monitor the voltages at the sensor. I wish I had such a box!.

XXXXXXX
X O X
X X
X X
X XXXXX
X X C X 5v
X X B X output
X X A X gnd
X XXXXX
X O X
XXXXXXX

I hope this makes sense.