Dan,
I took some of your advice today.....
I fitted the Speedo Ratio Box and tested out the connector on the gearbox and found which wire was the pulse wire.
I then removed the oddometer cluster and checked out the spaghetti that was the wiring behind it.
Found the wire which I was "pretty sure" was the one, (pink with blue stripe)
And then cautiously cut it. (I wouldnt make a good bomb defuser)
Wired in the wiring and took her for a drive to test it out before I put it all back together again.
Works fine, no need to run wiring through the body to underneath the vehicle and Im spewing I never did it like that with me last hilux.
Anyway, I fitted the unit just above the drivers footrest and screwed it into the cooling unit and nicely tucked all the wiring out of the way and checked to make sure under normal driving whether my foot would hit it.
Job well done for once