I'm in the process of connecting an auxillary fuel tank and trying to determine if I should mount the switching valve under the cab along the frame at the lowest point in the fuel system or under the hood on the fender well at the highest point in the fuel system. What are the pros and cons of either setup?

 

I dont know if there is an advantage to were its mounted. I bought mine used with an aux tank, and the switching valve is mounted to the bottom of the floor boards on the drivers side about a foot in front of the stock tank. It's up out of the way there, but easily accessable if needed. It works fine there and doesnt seem to pick up much road dust and such.
I am actually thinking of removing the aux tank, since I havent needed it.

 

I also have mine mounted below on the frame a little behind the stock tank. I think as long as you put it in a location where it's not too hard to get to(mine quit on me and needed to be replaced after 10 years), then it doesn't matter much.

 

I ended up mounting the switching valve to the bottom on the cab under the drivers seat just inboard of the frame. The switch is mounted in the lower left front corner of the center console. The disadvantage to this valve location is that anytime you need to remove a line, you get a diesel bath and end up draining that line but there just wasn't enough room up on the left fender well where I would have prefered to mount it. Oh well, hopefully I won't have to take the lines loose anytime soon.

Now my only concern is whether the 1/4" hose barb that I used to connect the stock fuel line will restrict the fuel flow too much. Don't want to starve that pump. Guess I need to get a fuel pressure gauge installed and see what the lift pump is putting out. It never ends, does it?

 

See if it's the same size that's on the tank. I'll bet they are the same and wouldn't worry much about it. It's kinda like that with the auto tranny lines too.