I have to add a couple of items.
first is there is a ground wire up under the dashboard, drivers side, up a bit, you have to look for it. MINE was connected, but the wire that was in the spade that is how it's connected to the vehicle was rotted and when I tried to pull the spade off the connector off, it literally crumbled in my hands
ALSO, if you have NOT replaced your battery cables, chances are high that they are several years old.
It's a cheap fix - generally less than $100. I got all mine made up with special made ends on them. But you can buy them off the shelf. Most cables are about $15 or less. I believe you need six of them, with the one that runs down to the starter and to the from Nato slave plug the longest ones.