Control LPT to switch on light in board?

Question

I connect parallel port pin (6,7,8,9) to lit in board, it is always on why?

Answer 1

These are data lines.

You need a program to change the values on the parallel port.

Google "parallel port" for lots of info on how to do this.

Answer 2

It could be hardware or software related.

Easy way to determine is to use an old DOS based program to switch the light on/off.  

If it does your problem is with Labview.  

If not get out a volt meter.

Pins 2 to 9, are data with 5v to represent on.  Check the output of the cable.  Check the input to your device by applying voltage. (3 x 1.5v D cells in series should do the trick)

Depending upon your results you may have to check your circuit design. You may need to isolate your light by powering it separately through a relay.