Actually, I misstated that. There's not really a "starter relay", per se, but there are three relays that in conjunction can cause you problems.
There is a dropping resistor on auto tranny vehicles that would prevent your vehicle from starting if it were damaged or unplugged.
There's a interlock relay if your vehicle has a manual tranny, which would prevent it from starting if it wasn't working.
There's an interlock emergency relay on MT vehicles.
There's also an orange safety relay on the passenger's side under the kick panel in front of the door near the floor.
There is also an inhibitor relay on A/T vehicles that would prevent starting it if the shifter is in any Drive position or Reverse.
The relays in question are located under the hood on the passenger's side fenderwell near the battery. There's a cover over the important ones. On a Pathfinder, in order from front to back, they are:
Horn relay
Interlock relay
Dropping resistor
Under the cover:
Bulb check relay
Inhibitor Relay
FI relay
Main relay
Fuel pump relay
NP relay(if A/T), Interlock emergency relay(if M/T)
The starter solenoid wire should black with a pink stripe.
Hope that helps.