CM 870 JAKE BRAKES

[yardie]

Just bought and installed a Cummins CM870 engine with CM870 ECM. Having some issues with the jakes brake. Keep getting fault code 2368- engine brake #3 driver output circuit open. Also jake brake is weak as I am not getting 100% or the 3 stages of engine brake. ECM is outputting to the 3 jake solenoids and INSTE shows brakes at 100% but feels very weak. So I checked jake brake harness and found only two wires for jake brake solenoid #1 and #2 nothing for #3. So I Pulled the rocker cover and to my surprise only two engine brake solenoid were seen as in the CM871 set up.
Does the CM870 head set up comes with two engine brake solenoids ? If yes how would I be able to get the full 3 stages of jake brakes if the ECM is outputting to 3 solenoids and i only have 2 solenoids. Is there a way around this? or What's the fix for this?
Thanks in advance for your suggestions and comments..