2008 Ford Explorer Code B1203 and B1204

Question

I replace my fuel pump in my ford exployer and the fuel gauge won't go past 3/4 when I fill the tank

Answer 1

Both code point to a problem with the Fuel Sender Unit. Either the fuel sender unit got disconnected during the fuel pump installation or the fuel sender unit itself is bad.

B1203 FORD - Fuel Sender Circuit Short To Battery
Read more: https://www.autocodes.com/b1203_ford.html

B1204 FORD - Fuel Sender Circuit Short To Ground
Read more: https://www.autocodes.com/b1204_ford.html

Answer 2

you either has a bad ground on the fuel level sensor or the cluster 

see diagnostic procedures below