Jaybob provided a good overview.

The only thing I'll add is if you do confirm a bad ground to the relay, you may want to consider also adding a new secondary chassis ground lead to that socket to ensure a good ground. As these cars age, the resistance and corrosion builds up in the factory wiring underneath the sheathing and can drive you batty trying to chase down.

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)