Problem with LED bulbs in Lionel 6-12886 Floodlight Tower

The loop of wire between two lights is the clue.

I think they are 2 sets of series in parallel.

That explains your results- you put 2 LEDs in series, and by the wiring, they are the wrong polarity.

You put one light in series with an incandescent- it works.

with picture

@Bob Paris posted:

The four incandescent bulbs work fine but when I substitute four LED bulbs, the LED bulbs do not light.  I noticed that if I substitute two incandescent bulbs, then the two LED bulbs will light.  This mystery has me stumped. 

I will bet the lights are wired in series, this will cause the LED lights not to light.

More checking in the manual, yes, 2 sets of lights in series. The catch22 is the way they wired the sockets, the center contact to center contact. For AC and incandescent bulbs it doesn't matter, but for LEDS (key there diode- aka one way being part of the name) this wiring basically ensures you are setup for failure when replacing with common LEDs.

You would need LEDs with advanced circuits in the base of each bulb for full rectification from both AC directions to the LED and even then, because in series, maybe even an advanced current control circuit for the LED.

Otherwise, using normal cheap (and they may not be cheap $$ wise) but simple LED bulbs that are nothing but an LED and resistor- you need to rewire the system for all 4 sockets in parallel.

Edit- oops, hit send early

The manual https://www.lionelsupport.com/...ents/71-2886-250.pdf

This diagram again shows sets of 2 bulb sockets wired in series, but the center contact of one socket, to the center contact of the second socket.

I mean I guess a person could try unsoldering the LED and resistor in 2 of the bulbs, reverse the polarity of center to outside on the bulb base, and keep track of those 2 and use one per series pair- maybe that works.

Great catch guys! 

I've used lots of LED bulbs in single-bulb applications, so have never run into this.  Hope I can remember it if I encounter it in the future.

I also have the 6-14155 reissue of the #395 floodlight tower.  It appears to be constructed and wired differently than the 6-12886 and does not have this problem.  Thank you Vernon & ThatGuy for the help.