Do you have the intake off the engine?
You don't want to drill and tap an intake manifold while it's on the engine. All the filings and **** will go right into the engine.
The instrument panel/dash lighting is controlled through a field-effect transistor in the smart junction box, and the dash lighting is mostly LED.
I am unsure if you can feed aftermarket gauge lighting from this circuit without causing problems.
If anything, I would use the parking lamp output from the SJB, as this is designed to support the load of an incandescent light bulb.
In connector 2280D in the SJB, on pin 20, which is violet with a white tracer - is 12+ with park lights on output to the cab roof lights, or if not equipped, you can use pin 6 in connector 2280E, also violet and white - output to rear parking and license lamps.
Just my .02
Transistor driven circuits in the smart junction box typically do not like any extra loads on them, and the careful monitoring of the circuits by the junction box may show the extra current load as a short circuit and shut the circuit down using the programming in the module, which will likely cause you unwanted grief and require clearing of diagnostic trouble codes with the appropriate scan tool.