[MattEmily]

I agree with PRangerX that I don't believe there is usually a second in command except in some cases.

Alien Rangers = Aurico was because he was basically a field leader.
Space = We could say T.J. was a second in command because he was the one that came up with the plan to try and trick the Psycho Rangers by painting their suits blue.
Time Force = This was basically the same as the Alien Rangers, Red was second in command since he was the field leader unless Alex was the Red Ranger.
Wild Force = Taylor was second in command once Cole became the Red Ranger.
Dino Thunder = There really was no second in command even with Tommy there, he just allowed the others to decide things in most cases and he went along with them.
S.P.D = Sky was second in command for the B-Squad. Jack became second in command once Cruger became a Ranger. Bridge became second in command once Sky became the Red Ranger.
RPM = I would personally say that Summer was second in command since she actually took charge once when Scott wasn't around and Dr. K actually acknowledged her as taking charge.

2. Like PRangerX said Red usually leads in most cases including in the Sentai series but this wasn't always the case. Kakuranger's Ninja White (our White Alien Ranger) and Timeranger's Time Pink (our Time Force Pink Rangers) were leaders.
Also Gekiranger (our Jungle Fury) did not have an official leader until like halfway through at which point Geki Yellow was appointed as leader.

Also as we know Jason was the leader in MMPR until Tommy became the White Ranger.
Rocky was never second in command despite being the Red Ranger in MMPR.

T.J. wasn't the leader for In Space he just took charge a lot since Andros didn't know how to work with a team.

In the case of Nick and Daggeron it made sense. He was never called a leader but Nick was the Red Ranger and did take charge until Daggeron came around. It was Daggeron's responsibility to basically mentor them so he became the new leader.