Thanks Kaz.

I was a bit thrown by the TCS light staying on - always on when the ignition was on, and you are right, I should have gone through the revised procedure to clear the #13 ABS code as required by the upgraded ABS. Apologies for not figuring that out myself. So I did that and it cleared the code.

But the TCS light was always on with the ignition P2 or engine running, regardless of the SCS connector. I noticed that the clock wasn't on and also that key fob activation of the alarm wasn't working. The clock fuse had blown. I replaced it and the TCS light is back to normal.

Phew! I scared myself to death looking at all the inputs to the TCS (lateral acceleration, steering wheel angle, throttle position ...) and wondering if one of those had gone bad.