Are Proto2 bulbs AC or DC?

Marker lights have LED's on the schematic I have for a PS/2 locomotive, so I'd expect DC.  They are supplied directly from the PS/2 electronics with no resistors or diodes.

These are the ones in the Proto2 upgrade kit for a Proto locomotive.  Would the conversion kit be the same as the other PS/2 ... DC?  Would it make a difference to LEDs?

It does make a difference to LED's, they don't like more than 5 to 7 volts reverse voltage.  A 6V AC signal will have a peak of around 8.5 volts.  I'm pretty sure the kit is the same as other 3V PS/2 devices, at least that's what I've been told.

Light bulbs don't matter.  For the LEDs they run on pulsed DC.  There seems to be several variations in the Marker lights, but they are LEDs.  I have seen series wiring, and parrallel with a resistor under the heat shrink.

The main key is using bulbs in the light circuits and LEDs in the LED circuit (Markers and beacons).  This is all for the PS-2 obviously.  PS-3 are LEDs all around.  G

Switching over to all LEDs during the conversion to Proto2, using ones from say Evans Products, doesn't sound all that straight-forward ... maybe I better stick with what's in the upgrade kit instead of converting.

Replacing a bulb with the Evans design LED shouldn't be that bad, wire it right were the bulb goes.  The Evans stuff has protection for the LED and the current limiting resistors as well.

I heard the LED has to have the right + wire going to it's + wire, and the same for the - wire.

How does one tell which of the two wires is the + and which is the - wire, for instance the GRN/GRN pair for marker lights?

Well, depending on the Evans design specific product, they will work either way.  Many of them are wired with a bridge rectifier so they'll work for AC or either polarity DC.

FOR BULBS: It is not the GRN/GRN wire of the light that matters it is the color of the wires at the connector that feed the GRN/GRN light.  Normally in upgrade kits, the Purple wire that feeds the Various light bulb connectors on the 12 pin connector is the common Positive Voltage.  Again, this doesn't matter for normal bulbs.

FOR LEDS: If you look at your LED bulb harness in the upgrade kit, the red wire of the LED harness connects to the gray common wire of the LED connectors.  So the gray is the common Positive voltage for feeding the LED lighting on the PS-2 boards.

I guess back to your original question, which was about the board more than the bulb.  The PS-2 board converts the track AC to DC.  DC is used on all the circuits.

So if you connected a LED and it did not light, you could just reverse the leads.

A good example of this is PS-1 systems with a beacon.  It is a universal 2 pin connector.  If you plug it in and the beacon doesn't flash, you just flip it to get the right polarity.   G