1990 mustang gt no power?

[ddt4436]

Now what happens is when I turn the ignition switch to "on" and jump the selonoid at the fender the starter will not turn, but when I have the ignition in the "off" position and jump the selonoid then the starter will run. I already replaced the key switch and ignition switch 3 days ago.

 

[LarsD]

in the trunk on the drivers side right behind the taillamp. even more suspect would be a bad fuel pump relay. not sure where it is on the 90, but I am thinking its underneath the drivers seat.(it moved throughout the years)

if you havent done it yet go through Jrichkers Cranks no start checklist. it will seriously save you a metric butt ton of time and money.
Cranks OK, but No Start Checklist for Fuel Injected Mustangs - Mustang Forums at StangNet

It's under the seat on my 91, so I bet it's there on a 90.

 

[ddt4436]

Any more suggestions? The starter will try to crank if the solenoid is jumped but will not with the key. I replaced everything except the starter which I think would be good cause it's trying to crank. I have the mini starter by the way.