Factory Rev Counter wiring

[XBRIT]

Hi Guys,
When I purchased my 72 Challenger late last year the vehicle came with a regular AC dash, but it was modified to a Rally dash (sitting on the back seat) The guy who modified the dash to a Rally did a superb job. When I fitted it and plugged in the electrics to my amazement every thing worked, except the rev counter. It looked correctly wired behind the dash but of course there is no connection to the coil as the vehicle had no rev counter from the factory. What connection do I have to make for this to work.
The original build was a 72 318 auto with A/C. I have looked at the schematic in the factory manual but can not see a link. Cheers

[MEK-Dangerfield]

You will have to run a wire from the "-" side of the coil to the tachometer. One of the long screws on the back of the tachometer should have a tab where this wire would connect.

[XBRIT]

The wire is already their connected to the rev counter and goes to the firewall plug. I need to know the engine bay side connector pin number to connect a wire to the coil as the factory harness had no accommodation for this option.
Mike

[dodj]

The tach wire didn't use the bulkhead connector. It went through a grommet in the firewall close to the bulkhead connector. At least it did for '73. 

[XBRIT]

I think I found the tach wire, when I refitted the dash their was one solitary long wire with a connector on the end, Grey with a tracer. I pocked it through the fire wall. I can not run the motor yet, is thier any way I can check to see if the tach works without running the motor?
Cheers,
Mike

[Giveitawack]

The tach wire uses the #20 position in the bulkhead connector on my Barracuda -70. In the red ring in the diagram.

[XBRIT]

Cheers, for the schematic