Any white LED will need more

Any white LED will need more than 3V. That's just physics, nothing you can do about it.

You said "factory delivered"...

... So is this decoder a naked board, or a shrink-wrapped free-flating decoder?

If it's a naked board, look where the leads for the LED attach... there's probably a surface mount resistor near there. You might be able to trace the circuit , find the resistor, and either remove it and replace with a 0 Ohm "resistor" or just wire in before the existing resistor.

What is the solution?

If in fact the decoder only delivers 1.5 volts, and LEDs need at least 3 to function, what is the solution to replacing those bulbs?  Who’s decoder is factory installed? Is there a trace that can be bypassed to get the full 12+ volts thereby allowing use of an LED and resistor? Are there other functions on this decoder that put out higher voltage that can be used?  This has peeked my curiousity as I have not run across this issue…yet!

Tom

Look for a "14v" solder pad

Some OEM decoders in HO engines do have a place to get full track voltage, often marked 14v.  You will need to put a resistor in line with the LED.  I use 1K and 1.5K ohm 1/4 watt resistors.

And no, there is no such thing as a "white" (three crystal) LED that works on less than 3.7 volts.

Let us know what you find.  A local friend has an Athearn P42 with a factory installed Econami (I think) and is having similar issues.  I already told him what I told you.

Scott Chatfield 

Decoder type

Tsunami OEM Athearn GP40-2 is what DecoderPro is telling me.

This is the unwrapped board that snaps into place on type of the motor.  

Voltmeter only shows 1.5V coming off the Forward headlight and  positive common leads.

+14 hole

You see the gold-rimmed hole on the lower left of the board.  That's your 14V common.  You need to wire the LEDs' anodes to that, and the cathodes to the respective switched pads on the ends of the decoder.  Don't forget to add a resistor to each LED.

Remember,  you won't see voltage across those unless the F0 function (headlights) is on.

Scott Chatfield 

14v common

Thanks, I'll use that as the + common and wire them accordingly.

I appreciate the assistance Scott.