I used 2/O - 3/0 welding lead fine stranded cable for both the Pos. & Neg. cables, one each. No problem since. I did install the bigger starter and rebuild kit in the solenoid.
Yes from starter plug straight to thick black wire 4 pin plug.
The wire from relay to starter just goes into loom & out...it doesn't branch off to anything else in loom.
I said it b4 and i will say it again if the starter solenoid is clicking then all the safetys are working along with the relay. So either you're not getting enough voltage at the starter solenoid
(Witch i dought) or you have a starter problem. I would recommend another starter solenoid or if you bought that starter then try to exchange it for another one.