NS Executive F7 A-B-A Ditch lights (20-80007B)

This is a PS/2 set, right?  I'm surprised there's any 1.5V or variable voltage in there, PS/2 pretty much has 6V bulbs and the markers/class lights are LED.

Yes it is PS2 3 volt. I to was surprised by the 1.5 volt reading . Both the ditch light and interior light measured in that range. I listed headlight by mistake. It was interior light. There is a multi-wire harness (5 Wires) that runs from the slave board 8 pin connector to the Multi distribution plug assembly that is mounted under the cab interior. From it there are plugs for headlight, interior light, ditch lights, number lights and one for the coupler.

I thought about wiring up a couple of LEDS but for in my overdue reorganizing of the shop cannot locate any. Don't remember ever having White ones in that small of diameter. I don't think my customer would be amused with green Ditch lights.

Maybe I will try a 1.5 volt bulb and plug it into the interior light socket. If the bulb blows up no lose. If I blow the board it will be ugly.

Well I took another approach and measured the resistance across the bulb. 10.2 ohms. Measured new 6 volt bulb 10.7 ohms. They must be 6 volts bulbs. 1.5 are a lot less resistance. Plugged a new bulb in and the brightness looks about the same as the others with no Smoke. Maybe the board does not come up to full power until under load.

Now how do I put a 3mm bulb into a 2 mm hole. ARRRGGG. Sometimes talking about it is all that needed to wake up the mind.

Forest

Maybe I'm wrong here? (very likely).... or GRJ isn't explaining it right?

You can't measure the bulb voltage on a MTH board set like that I believe. It puts out the power differently than your meter will read.

Stan, GGG, etc., has posted about this many times.

I personally would use a small warm white bright LED if it will fit with a resistor attached ( around 300 ohms). The LED has to face at you to look the best. You'd have to clean out the hole with a bit I bet.

I put them in my G scale and love them. Yes those are bigger ones. They make smaller. New MTH PS3 O scale engines have them.

I have a pair of ditch lights from a PS2 GP60 that I replaced with LEDs. They are 10mm from end of plug to end of bulb, but I'm pretty sure they are close to 3mm. Let me know if they can help you.

Correct on the measurement, PS/2 uses PWM for the bulbs and any incandescent will have a 6V rated bulb.  I had to buy a bunch of 6V 2mm incandescent bulbs on eBay when I needed them for PS/2.

They are 6V bulbs.  You need to use a drill to break up the glass left in the lens to open it up.  But MTH did have small diameter bulbs used on some models.  Do not remember part # off hand, but think it is in the generic parts list Techs get with binder.  Some diesel with Ditch used them, and probably a few other applications.  G

After looking this over closer I am convinced that who ever worked on this before glued the bulbs in along with the Walthers Goo. The 2 mm hole was the inside of the light bulb. I drilled them out with an 1/8" dill bit. Used an exacto knife to clean it up a little. Bulbs know fit. I don't have any White LED's at the moment so put MTH replacement bulbs back in after figuring out the voltage part. The one lens came out making it easier to clean up after drilling. The other lens is cemented pretty solid.

The one bulb needed a small spot of Goo to hold it in place. Just enough between the wire and back of lens socket. The other fit very lightly snug and needed nothing. Now just need to put the shell back on. The front end clearance between the ditch lights and the number board bracket is very tight.

I found  an E-8 A-B-A parts diagram that I saved to my computer years ago. It used the same patch board set-up and used all 6 volt bulbs. That's when I got the idea to measure the resistance on them.

After this it is going to get a smoke unit upgrade and all should be well.

Forest.