After I did my AOD to Manual trans conversion almost 10 years ago, I have swapped the Auto trans harness to a manual one. But I have always kept the '87 Auto trans O2 harness in place. In that time I have gone between using a C3W auto ECM and a A9L manual trans ECM. I have yet to experience an ECM failure with the A9L still using the '87 auto trans O2 harness. So is it really necessary for me to swap to a manual trans O2 harness when I use the A9L to make the trans swap complete?