Tacho connection to dash

[Mordred]

The defroster relay connection is one of the few to go up the front and is good because the current draw with the tacho pulse is very low.  You would need to use it to run a relay to do starter work as the voltage drop would be too high over that distance but I like your thinking.  The other way is to run a trailer cable front to back and you get 7 cores you can parallel to get greater current capacity. 

The 8 pin connector has a wire on only one side and I just added a connector to use it.  I just used the little ringed numbers on the wiring diagram in the Bentley to work out where the pins connected to.

Adrian