In my opinion, NHRA could care less about the light in your dash. That is a moot point. What happens is if you push the pedal and then set the line lock and then release the pedal the rear system goes to zero pressure and then the spool will slide over grounding out the connection to the light turning on the light. But when the spool activates or slides it will drop the front line pressure a bit and this may cause the car to roll when the driver expected it to stay put. OR, the rubber "O"-rings on that little spool could leak or fail dropping the front line pressure to or near ZERO and then the car could lurch forward hitting a track worker or one of your crew. So at that point you are relying on a 40 year old "O" ring to hold front line pressure and it is not the best idea. I took one of these apart and it was NASTY inside.

To plumb it properly you would keep your stock front line from the master to the dist block and then plug one of the front outlets from the dist block and then take the second one to the line lock and then out of the line lock to a "T" and then to the front brakes. They do make plugs for the unused port on your dist block.

I like to use the hurst line lock or the summit one scourced by hurst because it has several ports and actually takes the place of the dist block.

Here are some pics but it is hard to see.