Hi friends.

I’m hoping for some help as I have a starter issue.

My starter is working just a bit slow to get going.

But, when I went under the van I found three wires but only two were hooked up.  The third wire and the thickest of them was not connected as the connector had come off. 

So, what is the thick wire for?  As far as I know everything was working. 
All lights and even the house batteries and the starter and the alternator. 

How could it work with this not connected?  And what are the usual three or so wires connected to the starter?

Eric Caron 
84 manual trans.