Tony, this is the topology published by MMC for the Roadster showing hookup between ECU, BCU, instrument cluster and diagnostic socket.

[Linked Image]

It shows high and medium speed CANBUS and confirms your mention of two terminator resistors across CAN high and low and on each speed, these to prevent reflected signals at termination causing data corruption when bounced back. Since the GDI +4 uses similar BCU, albeit with the VDO master gauge system for instruments and no medium speed CANBUS used for same, it seems reasonable to assume it has otherwise a similar hookup.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone