There’s one thing you can do as a backup officer arriving at a vehicle stop that the primary officer will really appreciate because it helps protect him in three ways. That’s to turn your headlights off just before pulling behind the primary’s patrol car and leaving only your parking lights on.
This:
1) prevents your headlights from silhouetting the primary officer if he is approaching the suspect vehicle;
2) prevents a set of headlights from shining in the primary’s eyes if he is returning to his unit;
3) prevents your headlights from lighting up the inside of the first unit and potentially blinding him if the primary officer is seated there when you arrive.
Don’t we shine our headlights/spotlights on the suspect’s vehicle to put its occupants at a disadvantage? Why use our own tactics against each other!