I prefer to make a connection in the less harsh interior enviroment and since the wire is already inside, the extra wire and it's added mass and potential for shorting aren't necessary. I always keep it as simple as possible. I added a shiftlight and tapped into the signal at the gauge because it was the closest. The tach signal can also be picked up at the cruise control module or the auto transmission control module. I THINK the tach signal is a square wave and the voltage drop due to excess wire won't affect the reading because of this - the tach reads pulses not voltage.