I didn't know the instrument cluster already had 100 Ohm termination. I agree 100 Ohms is low... the OEM MCM is driving 50 mA into METSCI. Interestingly, the minimum guaranteed driver output current is only 35 mA, so Honda is using the LT1487 above the linear specification.The instrument cluster already has a 100 ohm resistor across the two lines, so I wasn't planning on adding one. From Honda's design it's clear the cluster was never intended to send data, only receive it. But I think I might be able to make it work.
100 ohms is pretty low - I'd wish it were higher. Unfortunately, I can't expect a user to replace that resistor. It's surface mount, and it could cause some issues with a stock BCM if it were changed. I'm not sure we'll get good transmission with 220 ohm series resistors on the lines. I think you should probably switch to a 100 ohm termination resistor to match the stock setup.
There shouldn't be bus contention anyway because Pegasus will be a slave device - it'll only send anything if you send it something first and are waiting for a response.
Also, from the datasheet, loading the LTC1487 to 50 mA drops the differential voltage to just ~1.65 V typically. LTC1487 only requires 200 mV magnitude between A,B for guaranteed signalling. I hesitate to add any more termination resistance because Honda is already driving the LTC1487 out-of-spec. However, leaving my side floating will almost certainly prevent you from reliably communicating with me (I'll 100% be able to communicate with you, as OEM).
I'll add a SPARE parallel termination on my end and remove the series resistors I mentioned previously. Maybe you can talk to me with 2 kOhm termination on my side... we'll see .