Try applying 12 volts to the green wire going to the starter soleniod. If the truck starts right up, perhaps the starter relay was never bad to start with and the problem is in the ignition column (the key start terminal on the column.)
If this is the problem, it may be easier (and cooler) to wire up a push-start button in place of the hassle of trouble-shooting the column.
Many jeeps get such a push-button because it makes serious off-road rock-crawling easier.