OK here is a copy of the diagram for the DLC. Terminal 16 should have power. Now if you have power and still no communication, then it is highly likely that a control unit may be bad. You would need to disconnect all control units, Engine, Airbag, ABS, Transmission etc. Then connect one at a time to see which one is not allowing communication. Since all control units share the K-wire if one shorts out, you have no communication with anything. Also locate the K-wire on the DLC and using a volt meter see if you do not have a short to positive. Check for voltage at that terminal. Do not use a light tester for any electrical tests on this car, can cause a feedback issue and damage control units. Let us know what you find for further.
Click here for diagram
The bike in the picture is a Harley Electra Guide. Similar to the Road King but fully dressed. Take it pretty much every were I go. Don't drive a car too much.
This is the ground wire for the speaker, they may have joined another ground some were else, this will not effect the scanner. The only wire that will affect the communication is the K wire. The other item if there is not power at the DLC terminal 16. Something is killing the communication on the K-wire. Since it is a digital signal a short to ground or short to positive will kill communication. Most of the time when a control unit fails it shorts it to ground.
I recommend you try this really quick and see if this helps. You can try rebooting all the control units. Sometimes this may work. Disconnect the battery negative first then positive with both cables disconnected touch them together. This is called a capacitor discharge. Once you have done this reconnect the cable, positive first then negative. Make sure this done with the key off and out of the car. Be ready for the alarm to activate as soon as you connect the second cable. Once this happens just use the key and lock and unlock the car. You can use the remote if you have one.