here is a possible option for connecting the trigger wire to the reverse lights that are "pulsating" with the PWM:
H3FA-AU-DC12V Omron Electronics Inc-IA Div | Z3012-ND | DigiKey

this is a time-"delay off" latching relay, from Digi-Key. they sell it for about $50 a pop, but it might be the solution that the folks without the PDC might need.

Are there any electrical engineers outhere that can collaborate on this specs with me?