Drivers side firewall. Basically drain the canister, pull the top and remove the old filter w/o-ring, replace with new filter w/new o-ring, pop it back in the top and put the top back on the canister. Then let the fuel pump run without turning the truck on... maybe do it 2-3 times. I've actually just let the engine turn over 1-2 times without acutally cranking... this allows the pump to run for about 30 seconds. This fills the canister back up and then you're good to go.