Guys, I must eat some CROW!!!! First let me say that I did some research on the differential pressure switches. The total function of the switch is to turn a light on on the dash to alert the driver that there is a difference in pressure between the front and rear brake circuits. There is no other purpose. These switches were Federally mandated to be in all automobiles by 1970. Therefore it is extremely possible that until that time some vehicles did not have them.

However, that is not the case for the 68 Barracuda. Today I checked my totally stock 68 and there is definitely a wire running to a location on the distribution block. I then compared that to my race car block and there is definitely a place that at one time I'm sure there was a wire connection. I bought my racecar about 1987 and there has never been a wire connected to that block. I therefore now agree that my 68 cuda has a switch in the distribution block even though it is not hooked up.

Now the question of legality arises. The stock dash from my racecar has been gone for many, many years as has the light which would have been activated by the differential pressure switch. The switch in my car can therefore serve NO function. Is my installation legal?? There certainly could be some question since the switch is still there in the block. However in the current configuration it makes no difference where my lineloc is plumbed. It could definitely be a discussion item with a tough inspector.

I don't understand why the rule is there. If plumbed in front of the differential switch when you locked the front brakes and released the pedal the light should come on telling you that the lineloc is working. If the light didn't come on something is wrong.

Also I for the life of me cannot figure out how to plumb a one line line-loc with 2 lines. Maybe there are units out there that can do the job but I have never seen them. There would have to be 2 inlets and 2 outlets. Most are not like that. I know my 2 TCIs aren't.

Anyway, I stand corrected about the distribution block on my car, I was wrong. However I won't change the config which has been in use for 15 yrs, but I will delete the distribution block when I plumb in my new line-loc in a couple weeks, I just need a few more connectors.

And just a sidenote I am very aware of why the NHRA has developed the rules they have. I started racing altereds in 1955 and have seen the rulebook grow from the original few pages to the almost 300 it is today. And, I agree with 99.9% of them and even implement those I don't agree with so my car will be correct.

Gearhead01, when you release the pedal there is definitely a pressure drop. The front brake system has pressure but the rear brake system pressure drops to zero. That's exactly what is supposed to happen. However if the line-loc in pre switch the warning light would come on. That doesn't mean there's an unsafe condition. It means there is a pressure differential. I assume NHRA wants the light functionality to be as designed and that would be a problem if it comes on.