Vacumn Leak - need help!

[slamd58]

Guys I have a vacumn leak behind the dash. It gets worse when the top air/heater control is moved from inside air to outside air. I have traced it from a vacumn canister in the engine bay (bolted onto the heat/a/c exchange box on the left side of engine bay). I can remove the line in the engine bay and the leak stops. I am assuming this line goes to the heater/ fan unit under the dash. However I can't see where it goes...... to much stuff up there. Does any one have an idea of where this line should attach? Anyone got a picture of there dash out but the heater box in place (if that is possible).......

thanks for any help

p.s. got all the leaks fixed on my blazer and had some engine work done...... (the 454 is smooooooth now). Also, had the muffler shop extend the pipes out to the back of the blazer instead of dumping underneith..... It is much quieter and sounds awesome.... I know I'm disappointing some of you who work on your trucks..(and actually still love doing it...I'm jealous) ...been there done that..... don't have the time since I just bought the Coldwell Banker R.E office here in K-falls....