Starter wire from ignition switch: color and access.

[Neroado]

2018 Silverado, 5.3.  I want to install a remote relay kill switch to my starter.  I'd like to hide the entire installation under the dash, so I need to locate the starter wire from the ignition switch.  Can anyone tell me what color the wire is and what the best place is to access it under the dash?  I'm hoping I can splice the relay/switch into an actual old school wire without going through the tiny BCM wires.  I'd rather not have to access the starter wire from the engine compartment.

[tbarn]

Unfortunately, the "big" wires for the starter are all located under the hood. All the rest are 5v, communication wires, BCM,  ECM, and under hood fuse block with a pcb relay.