David,

The vac switch is inserted into the back of the injection pump. If you look down between the injection pump and the oil filter housing you'll see a round cylinder sticking out of the pump. It protrudes about 1.5" and is about 2 inches around. Brown with blue stripe vac line from firewall (and start switch in dash) is attached to the top.

You have to move some vacuum hoses - I also removed the white plastic vacuum switch that sits on the injection pump, over the shut off valve. There are (4) 6mm bolts (10mm heads) in a "collar" plate that holds the switch into the back of the injection pump.

It's pretty easy, just have to take your time working the wrench. Trick is getting the "arm" of the shut off valve hooked in place when you insert the new valve. I got it first time, used my hand vac pump to be sure that the shut off was pulling the lever inside the injection pump. Be careful with this as one thread warns that you could jam injection pump to full throttle...that would be exciting!

There are some good threads about how to determine if the shut off valve is shot - before you mess with it!

Part number from FastLane is D2020-11537, ,cost me $38.09 and was worth every cent!

...on to door locks, windshield and rear window seal, and then $ (ie; air conditioning!) Don't care! Love this tank! Fred