When running 2 fuel pumps besides my 255 in-tank I have now what is the second pump I'm looking to buy and where is it normally installed?

 

If you're referring to a T-Rex, or pusher pump, I believe it's located just before or just after the fuel filter in line. It's easy to mount, and a fairly straightforward install. But make sure you get one with the proper size fuel line input/output or else it will be fitting's city.

I found out the hardway.