Saab 900

My 1986 Saab 900 stopped running. I took in the battery and they said it was fine. After recharging I was able to drive it and get the charging system checked. The said that it was not the alternator, but the wiring. I noticed that the ground wire was shot so I replaced it. The auto parts store did not have the right gauge in stop (it is the only one within walking distance) so the tech there said that I could use two wires to get the proper voltage. I did that and it still will not start. The fuses look fine. There is a clicking sound when you try and start it, but it does not turn over. That was before the battery lost charge from sitting again. Any comments or suggestions (outside of retiring the car) would be greatly appreciated. Thanks

That clicking sounds means not enough voltage is getting to the starter.  My guess is between starting it and when you got the new cable(s) it may have run down and may need a new charge, or somewhere there is still a bad wire, contact or relay.  I don't think anyone can say from the information you have.

Well, you’ve improvised the ground cable (hopefully clean on both ends); now you need to check the positive cable.

Make sure the terminal is clean at the battery AND the junction terminal that should be located on the inner fender near the battery positive terminal.
The positive cable connects here with 2 other cables by a stud/nut that is under a plastic cover.
Remove the nut, clean all of those ends, and see if that helps.