[MrE]

Simon, if your BlueTooth is connected, that means at least 2 wires are correct on the J1939 harness adapter, the 12v positive and the negative. I'll assume that you have a diagnostic plug in your engine compartment also. Plug your harness adapter into the engine compartment diagnostic adapter and see if everything works from there. If not make sure that the harness adapter is wired correctly, that the CAN high and CAN low are mapped correctly. All the adapter wiring pin outs can be easily found on the internet. Worst case scinerio is you'll have to run a shielded CAN bus wire from your engine compartment to your cockpit and find a ignition controlled hot and a ground. They sell J1939 plugs for under $10, wire it up and lose the adapter.