DCS PS! to PS3 Conversion

You can run the cab lights, marker lights and firebox off of the headlight circuit.  You will have to make a 3 way splitter harness.

The marker lights will need a resistor.

That is typical as PS-2 or 3 upgrades only have one control able circuit for a light because of the 10 pin harness.  Since Premier engines have lots of lights, they were run off a CV board.  The conversion usually keeps that installed.  You could wire it into a light switch on the engine which use to be smoke as an on or off for the CV board.  Or go the mod David is talking about.  Though you start to approach the limit of the light FET at 3 bulbs and markers.  G

If you want to run all the lights off the headlamp circuit I reccomend switching to LEDs. I usually go with 3mm warm white LEDs. To replace the 6v bulbs with LEDs connect a 560 ohm resistor to the anode (long lead) of the LED and connect the resistor to the purple (positive) lead in the headlamp circuit. Connect the cathode to the blue (ground lead) of the headlamp circuit. By converting to LEDs the draw on the headlamp circuit is greatly reduced. I have run the headlamp, markers, number board, firebox, and cab lights as LEDs off the PS3 steam upgrade kit headlamp circuit without issue. The Blue Goose below was wired as described above. It's a PS2 5V locomotive that came to me with no boards or wiring, so I used a PS3 steam upgrade kit in it.

FWIW, I almost always dispense with the CV board and run all the lights from the headlight circuit for this very reason.  I use LED's for most lighting, but I retain the cab light incandescent, it does a nicer job of illuminating the whole cab.

Thanks to all who replied with the fix!