this would work
use the female end on the car and the male end on the tacho female is more insulated from shorts so it goes on the end that has power even when the device is disconnected
think of house hold plugs. the plug on the appliance has the sticky out bits. if the socket had them we'd all be dead.
the wires come through the plastic before you crimp on the connectors ........ !....check!
need to crimp and or crimp and solder, can be achived with pliers and a soldering iron if necessary
work out which way the connectors go in... before starting otherwise you may find you have it all the wrong way
pice of ground down hacks saw blade mounted in a dowel or a very thin crap £1 screw drive can be used to remove the connectors from the plastic if you make a mistake.
or get a bumper set of 60 connector tools off ebay or facebook advert and spend the day working out which one
see the little tab that sticks out from the body between crimp section and buisness end..... thats what holds it into the plastic
make sure they stick out before installation and bend em back to sticking out, if you have to remove and start again
Dave