If your Haltech dash display is using or has been updated to use the NSP software, you will first need to set it up to communicate with a MaxxECU, similar to the example shown in the "Third-party ECU CAN" section of this article: Sourcing data for dashes in NSP.

Also ensure that your Haltech display dash is correctly wired to an appropriate power and ground source, and that the dash's CAN High and CAN Low pins are connected to your MaxxECU’s CAN High and CAN Low pins located in the Superseal connector. 

Optionally, you can use an HT-130046 CAN adapter loom to plug the Haltech CAN High (white) and CAN Low (blue) wires into the ECU connector. This adapter uses a DTM-4 receptacle, which plugs into the CAN cable included with the Haltech dash display. Red and black flying lead wires are fitted to supply switched +12V and ground, respectively.