Read LED full size works, smd does not

[Martin Tellblom]

Hi,
Need help with my electronic skills (I'm a programmer, so my electronics knowledge is not so high)

This is my problem:
If I attach a potential free input around a LED and resistor a as in a picture below (green and yellow is the potential free input) it works (when the LED is on the binary input is closed, when the LED is OFF the binary input is open).

When I tries to accomplish this on a PCB with smd LED on it does not work the only difference is that there are 3 LED in a row (ie GND - Resistor - LED - LED - LED - VCC) .
Its the same voltage (+5VDC) in both environments).

Need help to understand why it's not working, and how I can get it to work.

[Martin Tellblom]

Found the problem myself
There was another resistor on the other side of the PCB. If I connect the cable there instead it works