As it was only receiving 11bit IDs the 2 LSBits in the IF1ARB2 register are not used. this meant that any message_id in the IF1ARB2 register that is less than 4 ie 00b, 01b, 10b, 11b was ignored and interpreted as a message ID of 0, any ID of 4 or greater was of course unique, in the above configuration.

Setting the bits in the correct location in the register made all the difference.

So in order to to answer my own question above. If I want to wind up the windows of the car all at the same time.

I set the Umask bit to "1" (to enable the mask) then I set the lower 3 bits of the mask to 0, so that only these bits are considered as a broadcast to the windows.

If I want to address only one window, then the mask is all 1's.

Easy when you know how.

Regards

Marshall