What lights can I use w ps2

MTH Use 6V bulbs.  The Lionel bulbs fed by a CV board are 6V, but fed from the TMCC or Track power are 14 or 18V.  They won't hurt the MT board, but the lights may not be very bright.   G

Normally the headlight and reverse light on PS-1 and some DCRU MTH engines are 1.5V.  The bulb will blow on the PS-2 board.  Many of the other lights are either track power or 6V plugged into a Small constant voltage board in the engine.  So anything from the CV board can stay in place.

For some RK, the problem is the headlight on a steamer is fed from track power.  So the screw in base is attached to chassis common (Outside rail AC).  If you attached your PS-2 wires to this bracket without isolating the base from the chassis, the AC would be fed into the DC side of the PS-2 board and seriously damage it.  That is why pinched wires that touch the chassis can cause damage to the PS-2 boards also.

The other issue is modifying the smoke unit so it doesn't try to get power from the chassis.   G

Of course, you can also convert many of those lights in your conversion to LED, you'll get brighter more realistic looking headlights, and all it takes is the LED and a 270 ohm resistor for the job.