OK, progress report time.
Pulled the 2-wire plug out of the main relay and turned ignition on - fuse blows
Pulled the connector out of circuit opening relay and turned ignition on, fuse doesn't blow. Turn key and engine almost fires but then dies.
Tested circuit opening relay and all the voltages & resistances came back ok. I then look at what the circuit opening relay does again, and go to the back to check my fuel pump relay I rigged up. One wire (blue and something) was loose so I reconnected it and put the connector back onto circuit opening relay. When ignition goes to "on" it's fine, but when it goes to "Start" it blows again. Then tried putting ignition to "on" and then connecting the fuel pump diagnostic switch (the yellow one in the engine bay). Sure enough, as soon as I connected it, the fuse blew.
So it looks like my fabulous mechanical skills have failed somewhere again. Am going to have to check and probably redo all the wiring going to the pump and maybe get a new relay too
