Some answers.

LEDs generally need resistors. 

Question 1  Where the resistor is placed, before or after the LED makes no difference.

Question 2  MicroMark has the answer.  You might try a single AAA battery (1.5 volt) then two AAA batteries in series (3 volt) and etc to bring them to a brightness you like.  Then you know the voltage to feed them.

Question 3  A question....   What voltage do you plan on feeding the strip lighting and how many LEDs in the strip you will use in the structure?

LEDs and resistors

This article may help

LEDS 101 (wordpress.com)

Resistors

OK, I get the idea on the little lights from MicroMark. and the article from the other reply gives me info on LEDs. The yard lights are NOT LEDs - so, I am inferring that the resistor will be attached to one of the wires coming from the base of the lamp and connect with the positive powered terminal strip and the other wire directly to the negative powered terminal strip like the MicroMark lights.

LEDs

Thanks for the article. I can identify plus and minus on the strip LEDs I am using which is usually a "string" of 4 to 6 "bulbs ?"

I may need to go back and rewire a few of the buildings that have LEDs to be sure they are correct. All building lights are hooked up to the accessories side of a spare power pack that are wired through a terminal strip ( one plus and one minus) closest to a group of buildings.

A couple resources

So there is a discussion about LEDs in the thread on Structure LED lighting and it has a reference to  The Magic of Lighting in O-scale Resource. The O-scale resource article is a bit dated as it refers to using 10% resistors, I think all new ones these days are at 5% or better tolerance and talks about Radio Shack! The O-scale Resource article has a link to a LED current limiting resistor calculator that is useful:  Current Limiting Resistor Calculator for LEDs

LEDs vs Lights

A normal incandescent bulb (grain of wheat or grain of rice) does not have a + and - lead and does not use a resistor to limit current. Stating the +/- and resistor everyone thinks LEDs.

If these are truly bulbs then the value of the resistor matters to drop the voltage from the supply to the bulb so you do not burn it out or it doesn't burn as brightly so you can extend the life of the bulb. It was common in olden days, to run 12 volt grain of wheat bulbs at 10 volts so it would last longer. 

For the MicroMark "bulbs" you need to provide a link to the item on their website for correct information from people on this forum. You should be able to find the information on the MicroMark website. For instance if it is these "bulbs"  from MicroMark  https://www.micromark.com/Miniature-Peel-Stick-LED-Lamps-Package-of-20 it states they work on 8 to 16 volts DC. The reason I put bulbs in quotes is while the description calls them bulbs (which many think of incandescent bulbs) they are really LEDs. I'll have to admit from the picture they look like incandescent bulbs not LEDs.

Your tower lights may be the same issue they may be called bulbs but are really LEDs if you can provide a product link others will be able help if there is nothing in the description.

Thanks

Makes sense now that I've read and re-read these replies. Will have to redo some of the wiring to buildings I have already installed the peel and stick "lights." Will cut one of the lines after it drops through the foam base; solder the resistor and slide a shrink tube over the connection. This should help them las longer as they are connected to the "Accessories" output from the stand alone power source.

David you state you are using the accessory......

....... side of your power pack to run current to your lights. Most accessory outputs on power pack are AC.  Be aware that LEDs require DC current and are polarity sensitive. Wiring them backwards will not hurt them, they just won’t light, but too much voltage will ruin them, hence the need for resistors. Most LEDs work between 1.5 and 3 volts. 
 

Peter

DC Current

Thanks. Will check the specs on the Troller power packs I am using.

What Yard Light Product?

 It would be interesting to see what yard light product you are installing?

I have some older style 4 light versions I will likely need to convert to LEDs.
(I just found a photo of those old ones I had left over from my old layout)