1990 Ford Bronco Turns but won't start, fuel pressure probl

I'm having the same problem as mentioned on the Dec 1st diagnosis question. I knew about the ether or starter fluid method. It does have spark. I tried with the help of a friend to see if the fuel pump was pressurizing before turning it over and got no responc from the pump. So thinking that the fuel pump was out, we replaced it. We replaced the fuel filter at the same time. When installed and we tried to see if the pump would charge, it did. We tried to start it and it tried to kick over but didn't start. Then discovered that the new pump wouldn't charge. Curiously we checked the old pump on the battery and sure enough it worked just fine. So why isn't the pump charging when I turn the key into the on position? We think that the battery is low from trying to start it before we changed the pump and the pump isn't getting the charge it needs. But if the pump was fine before why woudn't it start? NEED HELP on this one, Thanks.