The eec relay supplies power to the computer system the ground is needed to energise the coil to work the relay. The ground on the radiator support is for the eec relay. If the relay has 4 prongs the two small ones are for relay power. I have used a no.10 wire with two male prongs plugged into the relay slots the vehicle started and I went to ford and bought a new relay. I had a loose ground on my 1984 t-b and it wouldn't start. Somebody else on this forum with a bronco did the same as you when he tightened the ground it started last week.
All grounds I listed are for the computer.