• Where is the wire for the trunk/hatch pin and what color is it?
  • The wiring sheet Crutchfield sent for a 1993 Nissan 240SX says it is red and the location says “sw. or light in trunk.”
  • Does this wire run to the front of the car or do I have to run a separate single wire from the trunk to the front of the car?
  • Among all the wires running on the driver’s side close to the door (see photo), there are two red wires. One is separate and the other is loosely twisted with a green wire. I tried the separate one, but it didn’t work. Is the trunk/hatch pin wire among these wires?

The Red wire they're referring to is in the trunk, it connects the lamp to the switch. There's no other place to get a trunk signal. See EL-52 here (pdf page 938):
https://www.nicoclub.com/service-manual ... _240sx.pdf

Thank you. I got it working for test purposes with a wire dangled over the seat (using some spare wire to connect the red wire in the trunk to the green Viper alarm wire).

Do you have any suggestions for running the wire from rear to front?

In general (i.e., for the Viper alarm wiring connections), do you suggest soldering (vs. twist & tape; poke, wrap, and tape; butt splice connectors, etc.)?

The best thing for general wire-splicing is solder shrinks, they're God's gift to good wire repair. Been a long time since I touched a SXy interior, but front-to-back wires are usually best run alongside the Body Harness, which usually resides under the kick plates on either side.