Dimming Incandescent GOW bulb. Resistor or Diode.

MTH description suggests the stock item indeed has the solid yellow marker so I suspect you have an aftermarket lens with circuit board.

If the board puts out 5V and as there are no visible resistors you are probably correct those are GOW incandescent bulbs.

Either diode or resistor can reduce brightness.

But in a quick scan of GOW bulbs available they draw at least 50 mA. GRJ's LED board is limited to less than 50 mA max. If you could replace the GOW bulbs with, say, 3mm white LEDs then I think we could cobble together a way to use GRJ's board to directly drive the 2 markers as well as the LED strips. And eliminate the existing marker bulb board.

I'm fairly certain there have been OGR discussions on using LEDs to illuminate multi-color caboose marker lenses.

@Ward H posted:

This caboose also has nice marker lights, I'm assuming with incandescent GOW bulbs. They are not the solid colored plastic I've seen on other MTH RK cabooses.  They are powered by what looks like a constant power board that outputs 5V.

Just add a couple of diodes in series with the DC output, each diode will account for about .7 volts.  If you put three in, you'll have 3 volts, that should dim them.  If they're not dim enough, add another diode.

I took another look at the marker lights and discovered the GOW bulbs were just a snug fit in the housings and were easily removed.   A 3mm LED did fit into the housing. I have plenty of warm white diffused LEDs so today I'm going to wire one up and put it in the marker light housing and see how it looks.   If successful I'll go that route as adding two LEDs to the LED strip powered by GRJs lighting board will consume a lot less mAs than the GOW bulbs and that voltage regulator board.  

I'll be back with the results.

Many Thanks

Ward

If the LED fits, that's clearly the way to go, and as you say, easy to provide power from existing power supplies as well.

The 3m LEDs did fit. While they were marketed as being diffused, I still sanded the top flat and the sides. That evened out the light.    Wired them in series with a 1k ohm resister and connected to the LED light strip.

Before I removed the GOW bulbs and their power supply board the caboose drew 310mA.  After the mods the  caboose drew 35 mA.  Measurements were taken with the Bside ACM91 clamp on meter recommended by GRJ in another thread. It will be a useful meter.

Thanks John and Stan2004

WOW, those little bulbs were real heaters!

And that voltage regulator board they were attached to must have been drawing quite a bit as it got hot to the touch after it was on for a while.

The markers are a little dimmer.  The LED lighting board is at 20mA.  I may go back and turn it down a bit more.

Looks good, you can tweak the resistor on those to have them a bit brighter in relation to the cab lights.