You are making this a lot more difficult than it needs to be. There should be a 12V power source to each gauge. As stated above the senders are variable resisters to ground. The fuel sender for instance will be approximately 0 to 30 ohms. Approximately because truck gauges are not scientific instruments. They are a reference. I don't know what the ohm range is on the oil and temp sensors but they vary with the oil pressure and the coolant temp. If you get some resistance then they probably work.
As stated above, there is really no reason to go through all this. Hook them up and see if they work. If they don't, then troubleshoot.
