Question on hooking up factory tach wiring

[ricks70dart]

Installing factory tack in my 70 Dart rallye dash. I know the one wire goes to coil my question is where did they hook up the positive wire witch is supposed to be hot when key is turned on and where does the ground hook in at.wondering if they run to the back of fuse block where I see some connection points there? Haven't install dash back in car yet so have no power to check for a source.wanted to get this all hooked up before installing.

 

[VonCramp]

Installing factory tack in my 70 Dart rallye dash. I know the one wire goes to coil my question is where did they hook up the positive wire witch is supposed to be hot when key is turned on and where does the ground hook in at.wondering if they run to the back of fuse block where I see some connection points there? Haven't install dash back in car yet so have no power to check for a source.wanted to get this all hooked up before installing.

I am not saying this is how it's done, but I just ran the one wire to the coil from back of tach and mine seems to work fine on my '69 Cuda.

 

[4spdragtop]

Post pics of the back of the tach. One goes to coil negative. Can't remember the other one.

 

[RedFish]

2 wires on 2 posts. Posts aren't marked on the housing because the 2 studs are mounted on a small piece of board that will drop in either way. Anyhow...
The short stud is sender or signal from the ignition ( neg side of coil ).
The 12 volts on the longer stud came from a previously unused accessory fuse position.
Earlier fuse boxes didn't include the fuse clamp on the branch circuit side of the box where the wire attached.
I don't recall if the 70 model box had a fuse clamp provided there or not. I doubt it.
The most important point I can make is ground. The tach is mounted and grounded to the housing with 3 screws. The housing isn't grounded until its mounted. Feck that. Add a ground wire.

 

[1969383S]

Should be like this.

 

[Tony Fields]

Here's a wiring diagram
These are jpeg images....you can down load and blow them
up to a larger size to read them.

Hope this helps