Freightliner Coronado Detroit swap

[MommaBurt]

Here are the pinouts that you need.

Yes, you can activate the jakes without the engine running with Diagnostic Link. You could also supply a voltage to the wire from the ecm connector to the jakes to see if you can hear the solenoid click. DDDL will also let you see if the switches are working. Based on your post it sounds like you have a switch or multiple switches not working.