Originally Posted by 13BlackJKU
In the old days ignition switches used heavy contactors that could carry many amps, they used heavy gauge wires to power the ignition coil, alternator fields etc.
Todays ignition switches basically carry signals, not amperage. The pink/white wire you refer to is the run/start signal to the TIPM and wireless module; without it your vehicle stops. The blue/red wire is the feed from the TIPM to power the switch and it is protected by a 10 amp fuse.
The run/start signal is what gets the TIPM to power up the ASD relay for engine performance and the wireless module for vehicle security. This signal is monitored by electronics in the TIPM for shorts to ground, shorts to power, intermittent signal, etc.
This circuit is low current to carry signals, not power loads. GM goes one step above and uses a multiplexed 5V reference closed loop ignition switch which is more tolerant to low battery voltage during cranking. We add a power mode module with our swaps to control the sleep and wake cycles of the network to maintain functionality and avoid key off draws.
So lets say you tapped into that ignition switch run/crank signal wire, you connected it to power the light switch which in turn powers up the relay trigger. Then you add an incandescent bulb inside the switch to indicate the lights are on. You probably have 80-100ohm relay trigger consuming 300ma then up to 1/2 amp for the bulb(may be led) so now you placed a reasonable load on this low current signal circuit.
Now lets add the inductive kick generated when the switch is closed and the circuit complete, this can more than double the load on the circuit for a brief time. All this means you may interfere enough with the signal circuit to render a problem.
Years down the road the crappy Chinese switch supplied with your lights shorts out and your vehicle doesn't start.
I just had this situation with a swap where the customer added a remote start system and powered it off the ignition switch. After months of intermittent no starts he brought it to us and we removed the wire from the ignition.
The pink/grey wire I indicated is not a signal circuit, it is a power out from the TIPM designed to carry some load, but I would limit it to the trigger side of the relay.
Sorry for the ramble.