Is it possibles, say with jump leads from a running car to feed earth to the engine and a lead to the main starter lead or is it a pain to get too.
I just try to make as simple a direct connection to test as possible.
No way the battery to starter lead has moved when tightening so shorting to earth?
Years ago we had one that the starter lead got trapped in between the bell housing after fitting a clutch, can't be that though,it was when starters had a separate solenoid.
If you can follow the main leads all the way from the battery both to starter and to good engine earth then get someone to crank it a bit and put your hand on the leads and connections to see if any getting hot?
The leads in the photos are just the low power connections, what are the main ones like?
When you find it you will kick yourself it will be something really simple