Car won't start

1988 mercury grand marquis, 5.0, v-8, 119k original milles. Currently I am deployed but here is what happened and need help soon. Daughter drove car, parked, shopped. Went to start, no start, jumped it it started. Tested battery bad, changed alternater ignition coil and starter relay, plugs, wires, cap and rotor. Before all the parts were changed out. The battery was installed backwards ( reverse polarity) now I need a little help here, do I assume the ECM is fried, cuz we can't pull codes (with a tester) off of it and it still won't start. Or do I start changing fusible links, how can I test the ECM and where can I buy a new one for this vehicle. Thanks for the help