I have here a 03 Durango 4.7L V8 with a COP ignition system. Each coil pack has 2 wires which according to FSM one wire feeds all injectors and coil packs from a relay and one is a "signal" from the "coil driver" for Its cylinder. When I use my DVOM I get a voltage from the supply wire only if the other probe is touching the battery positive terminal. I'm guessing this means that it is shorted to ground. The voltage read is slightly less than the battery voltage. Truck runs but very rough, only pulls about 15inHg vacuum at idle, 18 ish at 3000 rpm. Also just finished repairing a vacuum leak on back of intake, a leaky fuel injector (fuel pressure was dropping KOEO), new plugs, and MAP. Pulled o2 to check for clogged cat no change. All coil packs had 1Ω resistance. Have spark at coil packs but it appears weak. Is the signal wire supposed to be hot and PCM supplies ground, meaning the supply is shorted to ground? If so, what's the correct method to hunt down where the fault is? Or is it the other way around?
When you use a multimeter to measure the voltage, one end connects to the battery negative (black probe) and the other to the wire to be tested.
Do note that a multimeter may not show all that is going on - the signal may be too small to register on a multimeter - an oscilloscpe would be better.
Also, a meter can be used to measure the voltage drop between two points so the black probe may not always be connected to battery negative.