Following your description, especially when we do not have a wiring diagram to look at or symptoms to think about. I can offer one suggestion for finding some voltage at a test point but not the right voltage. You know a wire cannot be shorted to ground if there is something on it, and the assumption is it cannot be open either, but one thing to watch out for when you have some voltage but less than expected, is to be sure you are taking your readings with everything plugged in. If you have a burned-open fuse link wire in a high-current circuit, the resulting carbon track inside the insulation will pass enough current for a digital voltmeter to pick up some voltage and give a false indication. In that case a test light would be more accurate because not enough current can get through the carbon track to run it, so you would correctly see 0 volts.
The same thing can happen in sensor and actuator / solenoid circuits due to a corroded splice. Multiple sensors will be fed from the same 5.0 volt source in the Engine Computer. That corrosion can be all that is between two broken wire ends, and a voltmeter can easily see some voltage if the sensor is unplugged.
Think of standing on a garden hose and blocking ninety nine percent of it. If the nozzle at the end is closed, you will still have full pressure there. Voltage is electrical pressure. If you open the nozzle, (plug in the sensor), and give the water, (current), a place to flow, you will drop the pressure across the corroded splice or the water will drip onto your shoe.
Perhaps that will modify your thinking about the voltage readings you are finding.
Thursday, May 12th, 2016 AT 9:50 PM