Big Problems.. Need help!
 

Last night i started the car it started fine.. but this morning when i started it .I found out that the car has lost power when im stomp on it ... and the light would seem more darker.. so i tought myself maybe a battery problem.. i went to some shop when i was in the parking lot the car suddenly seem to buck like it was going to die.. it suddenly die but the lights ,warning lighs were still on so i push the car to a parking space ,went inside the shop bought a new battery i replace it and when i put the key in ignition i didnt heard the huum sound of the fuel pump ... the starter wouldnt even crank ... so i call a towing to get home..i tried to figure out whats the problem... i check the battery ... the alt... when i put the key in ignition i got all the warning lights..the lights are working all even the heater.. but the starter wont seem to crank and i cant hear the fuel pump umm sound..so help me out the car sitting in my garage i need to solve this problem..one thing i did notice it was that the starter would still crank when i put power on it with a 12v source..help me out ! i need help :(

1992 Mustang 5.0 (91000 miles)

I'm not sure exactly what your problem is, but I'd start by checking the wiring by the solenoid on the drivers side fender and trace the wiring down to the starter.

your fuel pump cutoff (inertia switch) may be going bad as well. reset it and see if you can hear the fuel pump prime when you turn the key

this would have nothing to do with your starter not cranking the motor over though

sounds like there's more than one problem, i don't see how the fuel pump and the starter are linked in anyway?

problem
 

If this was my car, I would;
Check and proof both battery cables..sound and clean. Check for clean and tight ground connections to the body and block. Clean and check all connections to the selenoid.
Check the mount bolts on the selonoid to fender wall, make sure they're clean and tight. Unplug, inspect, then re-plug the wire harness from the selonoid...(dirty or wire pulled loose)
Proof the selonoid with a positive jumper wire to the battery.
Suspect your ignition switch at that point.
Aerostar syndrome.
Got one, been there.

Greydan is right on the money. Following his advice should solve your problem.

Take care,
-Chris

Thx Guy apreciate im gonna check this weekend i appreciate your help!