Marker Lights w/ Cruise Cmnd M on Lionel 6-28038 UP Consolidation engine?

Usually LED circuits are a much lower voltage that standard lamps.  A couple of volts v.s. 12 to 18 volts.  Also keep in mind that LED's are polarized. 

The CC-M only supports markers, and NOT any sort of incandescent bulb.  If you didn't wire them specifically to the CC-M, they're not running from there.

I'll have to disagree that it's not documented, from the CC-M manual.

Marker and ditch lamp outputs are provided on the Cruise “M” for locos with these features. The outputs are capable of driving LED’s only. Ditch lamps flash when the horn is activated (command mode only).

They directly drive LED's, one for each output.  The class lamps on the locomotive are indeed 2mm Lumex ceramic LEDs.

Oh sorry about generic, I didn't remember seeing that sentence about the marker lights. It's at the bottom of the first page.

The marker lights are in series with a 100 ohm resistor. And the voltage driving them is also the voltage across the headlight bulb which is incandescent. So it seems the voltage is just a little too low to light the LEDs now. The headlight and LED boiler front board is still plugged into the motherboard connector which was the stock setup. When I do a reset or program, the LEDs blink so the voltage must pulse higher to cause them to light...and to pulse the headlight.

I wonder what the power supply is now for the headlight/marker board. Does it change when the Cruise Cmdr M is installed? Does the motherboard R2LC power get pulled down a bit?

Nothing should change with the upgrade to M.  Headlights for a TMCC engine along with couplers, are AC driven from the R2LC via the triacs.  Same for early Legacy with the R4LC.  So if they worked prior, not sure why they are no longer working.  G

I'm with George, they should still be powered if they worked before.  I'd look for something knocked loose or a broken wire.  The headlight voltage should not have changed at all with this install.

Ok good. The headlight lights are on and the LEDs are almost on...wires look ok. Maybe contact resistance on the connector or something. Now I know where to look, thanks to all.

It's odd that the class lights only have a 100 ohm resistor, that would seem to put current through them.  The green LED's operate at about 2 volts, and if they're in series that's 4 volts drop.  You have an effective voltage of around 9-10 volts when running command, so the 6 volts is being dropped by the 100 ohm resistor.  That would result in 60ma loop current, three times the rating of the LEDs! 

If they're in parallel, you'd be dropping 8 volts across that resistor.  That would result in 80ma loop current, only double the rating of the LED's, but still WAY too much current.  Also, the resistor would be dissipating well over 1/2 watt, around .64W, so it would have to be a 1W or larger resistor.

My thinking is they're not wired directly across the headlight, or there is some other circuit supplying them.  From the Lionel Supplement #45, the wiring doesn't show any class lights. 

When I look closer at the Lionel parts breakdown, they have this board.  What is on the other side of that board?

CLASS LAMP LEDS / GREEN / W/PCB / 2-8-0 LOCO

I'll have to take the board out to be sure. It wasn't easy to see the color bands so I was able to reach the resistor with the meter leads and 100 ohms it was. I'm guessing about the wiring, but series LEDs and resistor in parallel with the bulb seemed the most likely. And it looks like that in the pictorial of the service manual. It's a 1/4 watt resistor. 6 volts would be ideal. There's another resistor on the bottom of the motherboard for something. I'll check it later.

Something else must be there.