LED wiring question

I take it this is a stock PS3 diesel.

This wiring diagram from the PS3 diesel upgrade kit instructions might be of some assistance.  To your point, it shows the LEDs going to individual 2-pin connectors, but that the "Ground" side is in common to all the LEDs.  So given the relatively low currents involved for LEDs, you could in fact use one Ground wire (not to be confused with outer-rail frame/chassis) in a tether.

Note that in the PS2 incandescent design you could add, say, a 2nd bulb and the brightness of both bulbs would be the same as the individual bulb; in other words overall brightness doubled.  This had to do with how the PS2 lamp circuit regulated the voltage available at the bulb connector.  But in PS3 the LED circuit is different - more akin to regulating current (though not precisely).  This means when you add a 2nd (presumably identical) LED the current will be shared and brightness of the original LED will drop.  If this is acceptable, so be it.  If not, then you could add $1 or so in components (transistors or an IC buffer chip, resistors) so as not to load down the existing LED circuits.  Different ways to do this, but probably involve accessing 5V DC to power the buffers which is available on several pins of the 40-contact harness.

A number of locomotives have doubled-up LED's, so I presume adding one more won't be a big deal.

stan2004 posted:

I take it this is a stock PS3 diesel.

This wiring diagram from the PS3 diesel upgrade kit instructions might be of some assistance.  To your point, it shows the LEDs going to individual 2-pin connectors, but that the "Ground" side is in common to all the LEDs.  So given the relatively low currents involved for LEDs, you could in fact use one Ground wire (not to be confused with outer-rail frame/chassis) in a tether.

Note that in the PS2 incandescent design you could add, say, a 2nd bulb and the brightness of both bulbs would be the same as the individual bulb; in other words overall brightness doubled.  This had to do with how the PS2 lamp circuit regulated the voltage available at the bulb connector.  But in PS3 the LED circuit is different - more akin to regulating current (though not precisely).  This means when you add a 2nd (presumably identical) LED the current will be shared and brightness of the original LED will drop.  If this is acceptable, so be it.  If not, then you could add $1 or so in components (transistors or an IC buffer chip, resistors) so as not to load down the existing LED circuits.  Different ways to do this, but probably involve accessing 5V DC to power the buffers which is available on several pins of the 40-contact harness.

Yes it is a PS3 diesel.. You answered my question... Thank you very much!!!!!

Make sure NONE of the wiring ever contacts frame ground, that will be VERY bad for the health of your PS/3 board.  The DC common for the board is NOT frame ground.

gunrunnerjohn posted:

Make sure NONE of the wiring ever contacts frame ground, that will be VERY bad for the health of your PS/3 board.  The DC common for the board is NOT frame ground.

Thank you,  John!!   My original question may of been phased too vaguely... I was curious as to why both the positive and the negative wires, from each LED was run individually to the connector and on the other side of the connector there was only one wire for each where they were plugged into the main harness.. I'm guessing this is done because of the fairly universal  main harness(?).... The wiring diagram that Stan posted answered my question.. My plan is to extend the current harness to the dummy unit and reposition some of the LEDs, not add LEDs and certainly not run any to the frame ground...

I just like to post that warning as an inadvertent short to frame ground with ANY of the wires will surely result in bad news for your PS/3 board.  The worse news is, if you cook a key lighting output, it's a board replacement as there is no separate lamp driver, they're driven right off the uP, so the board is toast.