Atlas GP38 w/QSI board -- ditchlight wiring question

John Joyce

Hello, I am fairly new to this group and I have a ditchlight wiring question.  First of all, I'm working on a pair of HO scale Atlas GP38 Gold's with QSI decoder/sound built in.  I found a file on the internet titled "Quantum 1 Lighting v 1.1.1" dated 03/21/2011 and it contains the following instructions, in Italics:

5 Ditch Lights Wiring
(All models except 131, the BLI AC6000)

The Ditch Lights use Pin2 and Pin3 on the connector adjacent to the flash memory chip. See the picture of
the Small Diesel Board in section 1.

On that connector Pin1, which is used for the Headlight, is the pin at the lower left corner of the flash
memory chip. If you turn the board over you can see there is a square pad under Pin1.

Connect Pin2 to the cathode of one Ditch Light LED.

Connect Pin3 to a 150 ohm resister and the resister to the cathode of the other Ditch Light LED.

Connect the anode of both LED’s to Pin5, which is +5 volts.

The cathode of an LED is the side with the short connector, the large part inside, and a flat spot on the plastic.


Attached is a photo of one of the actual boards in question.  My question is, why would only one of the two ditch lights get a resistor wired to it?  Is this a typo?  I'm not an electrical engineer but I would think I'd need one resistor per ditch light.  I do see which are pins 2, 3, and 5...and I found what should be the correct connector pin hardware on Amazon (these JST thingies).


Any help would be much appreciated!



While I'm not familiar with that particular decoder, after reading the instructions I agree with you that each LED should have its own resistor. Unless the output of function on pin 2 has a 150 ohm resistor already installed on the decoder.