An update to my previous question: Does anyone know what signal I should expect in testing for the reverse switch? I'm thinking it may have been the thicker of the two BL/GR wires and while I detected no trigger voltage on the wire perhaps I should be testing for something else.
Figured out the lack of blink is because I don't have a BMW Alpine based alarm. It's a Viper Python and it was set to Valet mode. Looked up the alarm and reset it to normal mode. Blinks now as normal, just about as bright as my E39.
Worthwhile update. My 325i is next.