Why do you need to power them all from one line? Real PS/3 boards have a ton of outputs for LED's. You can't parallel different types of LED's and expect them to function correctly. White LED's are not rated at 1.5 volts, I'm pretty sure the physics of creating an LED prohibit operating at that voltage, they operate around 3 volts.
According to the PS 3 install Manual there is only one plug that the headlight, number board light, and cab light plug into. Sorry yes my LED's are 3 volts. Am I reading the manual wrong?
What I'm seeing is individual wires for each of the lights. I see a headlight, taillight, interior, individual ditch lights for front and rear, individual MARS lights, and an LED beacon. If you're looking at the steam upgrade kit, those are NOT LED compatible LED outputs, they support 6V incandescent bulbs. You can use LED's for the steam kit, you'll need 220 ohm resistors for each.
There is a common ground, but the control is individual. Though things like Number boards are off one control line. Connector has the X2 in it. G
John, What I stated on my first LED replacement post will work great with steam or PS2 steam and diesel. I am not a fan of the PS3 diesel kit. That 40 pin connector can be worked carefully by those who are careful. I have seen several 40 pin connections that have bent pins and the rest gets nasty. If we could get at the back of the board it would not be a problem with the pins. Not so. They are a pain.
I will not do an upgrade when someone has played with the kit. I want to be the person who opens the box. I gulp when I see a member who purchased boards off the internet and some wiring. Do it one time and do it right.
BUY THE KIT.
I agree Marty, the PS/3 steam kit or any PS/2 loco is easy to add LED's to, and the connectors are big enough that they're easy to work with. The tiny 1mm pitch connector on the PS/3 boards is a PITA. It uses such tiny pins that it sometimes takes me a couple of tries to get a good crimp! I don't know what possessed MTH to go to such a fine pitch connector, it just invites problems! Lionel has the 1.5mm connectors on Legacy, and they're small enough. It's not like the PS/3 board HAD to be exactly that size, at some point you have to consider that someone has to work on these things!