I went through this. Whether you have the 490 option listed or not if you have the Bose system you need the 490 adapter harness. I complained to Bergeville stating that they needed to make this more clear but I think it fell on deaf ears.
"If I look at the current wiring and the Continental and Becker diagrams I see the problem:
My current wiring does not use the B block (apparently this is unused in HiFi option/Nokia cars)
My current wiring uses the C block pins to send the signals to the amp; the Continental diagram doesn't show that these are used for anything. It only mentions C4 and C6 for SWRC.
The only output to the amp on the Continental is the B block which explains why I have no sound because it is not being used
I therefore need a harness that goes from the Continental B block to the existing harness C1 block.
Reference
https://rennlist.com/forums/993-forum/896189-installing-the-continental-tr7412ub-or-radio-6.html
If the above is correct then the other/M490 harness should work. It also means that not having option code M490 does not necessarily mean that the simple harness will work."