I run the 12v power to every structure that I’m lighting and from there each LED is on it’s own, that is if a resistor is needed to adjust brightness it just goes in line with each LED, that way you can have several different LEDs all of different brightnesses all on one 12v supply line. When it comes to resistors and how I figure out what OHM I want to use, I just use the old trial and test method, that is I take one of the resistors in the mixed package I get off eBay (THERE CHEAP) and I just test clip one inline to the LED and 12v power a see how the brightness looks. I usually start with a 100 OHM resistor and go up and down from there to get the brightness I want. You do know that LEDs are power sensitive, that is there is a plus and minus side to LEDs and they will only light when the LED is powered correctly, that is if they don’t light you just reverse the power wires, you will not damage the LED if hookup backwards. I just take a test wire and hook it up to the 12v power supply, a test wire with some alligator clips to clip it all together where I can change out resistors to get the brightness I want before I solder it all together. I will say here, I do not use a model train transformer anymore I use 9v-12v power supplies sold on eBay, these are a much better way to control the voltage and the 9v will probably works better then 12v as 12v will be too much power and more resistors will be needed. Once again don’t get too caught up in this resistor thing, it’s not Rocket Science and you’re not going to burn the house down if you hook it up wrong. You can email me through the fourm and I will send you my phone number if you need to talk about this, I will be glad to help you.
Dimming when he turns the pot.
Isn’t the phrase… Brightening as Rooster stirs the pot? 
Ok, I’ll break!
Rooster, your pot / resistance / etc. description was excellent.
Thanks but it ain’t mine. I stole it off the internet and just reworded it a bit!
Oh c’mon, here I was about to crow further about your electronic prowess!!
Ok…since were talking about prowess can you tell me why the windshield wipers won’t work on this 2006 Volvo?
https://diagramweb.net/img/volvo-2006-s40-cem-module-wiring-diagram-3.jpg
They are broken 
Sure.
On ECM 4/46, I/O A-39 and A-68 are reversed, causing their square wave to be inverted to A-37 /A-55.
This happens frequently, and I’m surprised you’re not aware of this issue.
It not only affects your stinking Volvo, but sometimes the entire balance of the cosmos.
Please fix ASAP.
C
Does that explain why my check engine light keeps coming on? 
do you mean one of these “too-late-lights”?
just ignore it. when they come on, the damage is already done.
'cause some dumbass has disconnected the Blue (Bl, Bu) wire…
Probably not however I checked for you and it’s still there.
John that diagram is a standard light circuit. Rooster needs one for the windshield wipers. 
