Lock 7 Park

You can't park at Blatnick overnight. The parking lot by the lock (not by the boat launch) should be okay, as well as the parking area near the corner of Lock 7 road. I often park there for night rides.

Can i leave my truck here overnight to bike the trail

I just took a look and see that there is a nice sized lot near the locks and another a few hundred feet down Lock 7 Road that is a fairly large lot with trees around. There is another small (5 car) parking area right where the trail crosses Lock 7 Road. I see no signage prohibiting overnight parking. The safest way might be to ask/tell the Lock Engineer that you are planning to overnight your truck and ask for their suggestion (like do they mind if you leave your truck in the "Lock Area" lot). I would also think that parking in the lots closer to the Lock are safer than leaving it at the trail head parking area.

Now... how did I do that? I simply used the Interactive Map (which is Google powered) on this website. Using an overview viewing mode I found Schenectady, zoomed further in to find the Northway (I-87) to get my bearings, zoomed in a little bit closer and moved the map west until I saw Lock 7 Park clearly identified on the map. Then, I zoomed even closer and took the "Little Man" (in the bottom right corner) and dragged him onto Lock 7 Road and took a little tour. I could view the trail intersection, see the parking area, move further down Lock 76 Road more and more until I saw the parking lot and I could even move further to the end all the way to the Lock parking area.

Posting this here because I have mentioned how well this works when planning a trip or tour. I have scoped out camping areas, intersections of interest and anything else. This example was very cool as the Google Map vehicle went all the way to the end of Lock Road -- not always that lucky, but what a fine example of how you can use the interactive map with "Street View" to see what is happening at ground level.

I've ridden by Lock 7 after sunset with my bike lights and headlamp and have seen people with their cars parked hanging around the parking lot at Lock 7 who seem to be doing the usual things; talking, smoking cigarettes, drinking beer. They didn't seem to be hooligans or seriously partying or anything like that. Make sure you lock up your vehicle and leave your roof rack empty.
Going west at the top of the hill is a small parking lot at Blatnick park right next to the road where cars are going by all night and cops are circulating from Knolls. That might be a better choice. Other choices would be the parking lot further east at Lyons Park which is less isolated than Lock 7 and has more activity. Farther west is the large lot at the new Casino. This is patrolled, well lit, and cars are routinely left there overnight. The bike path there is all new, goes along a berm above the river and then down into the Stockade. It's quite nice.