I would move that power tap to a switched source of 12 volts. The TPS does not run on a full 12 volts and this could be your problem, it may have damaged the controller .
What you measured is about right on that TPS wire. Also if you are getting that voltage on full throttle and less at the idle position, you are on the "OUT" side of the TPS circuit, not the in side which isn't a good thing. The ECM reads that voltage that comes from the TPS to govern many functions of the engine management system. There should be nothing extra hooked into this circuit.
What you measured is about right on that TPS wire. Also if you are getting that voltage on full throttle and less at the idle position, you are on the "OUT" side of the TPS circuit, not the in side which isn't a good thing. The ECM reads that voltage that comes from the TPS to govern many functions of the engine management system. There should be nothing extra hooked into this circuit.