[C320-list] Ignition switch wiring - help asap please

[Graeme Clark]

I'm on the boat reconnecting the engine instrument panel. I left the manual and wiring diagram at home!
Basic connections seem simple enough matching colours on the block connector
But when I turn the key there's a short and the engine fuse blows
Multimeter diagnosis shows that the thick purple wire seems to be a ground wire and thus I figure I may have midwifed by key switch as this connects the thick red (12v supply) to the thick purple and thin purple with black stripe
The latter obviously supplies power to the engine instruments
I assumed the thick purple from jeyseitch connected to thick purple from engine loom at chocolate block - hence the short
So what DOES the thick purple connect to and why is it there as well as a thin black ground wire?
Very confused!
Graeme
1996 #366

Sent from mobile: please excuse typos etc.!