68 Charger 440 R/T Tach wiring

[Roger S]

Hi All

I am currently wiring a new Dakota digital VHX dash complete with all integral gauges.All the new dash control panel requires for the Tach is mains power plus a Signal wire connecting to it, the 12 volt power is the easy bit.

The problem is my old Tic Tac Toch has not worked in my ownership and appears to have had the harness removed leaving only a 12 volt grey wire supply to the centre of the gauge. This still has 12 volt permanent power. At some point a Mopar B Series electronic ignition system has been added and wired exactly as the attached images.

Question do I introduce a new signal wire from my new control panel onto the neg side of the coil on top of the current black with yellow tracer wire from the electronic ignition module ?
This is what the Dakota instructions say, however they make no mention as to what to do if you have an electronic ignition system fitted, there is no marked provision for Tach on the electronic ignition module like you would find on say an MSD system

I do not want to fry anything as the new Dash cost an arm and a leg.

Any help would be much appreciated.

Thanks

Rog

[Dave999]

if it is tach that worked off the flyback pulse from the coil primary originally there is no harm in running a new wire from coil - to the input on the tach

if it is a modern tach designed to run off a 5 V signal, pulse or square wave output from something like an ECU or an electronic ignition module or switcher connecting to coil negative will break the tach.

once you know the kind of input you should be ok and you may find it is switchable. the switch will introduce some kind of resistor and capacitor network to stop the 100s of volts flyback from the coil damaging the "I expect a 5 volt signal" input

tach may also need to be switched to 8 cylinder operation

or you will need to make or buy an adapter dakota sell one

or you use the tach input into the VHX control and you set it to coil negative input rather than ECU or module 5 volt

if this is what you have http://www.dakotadigital.com/pdf/vhx.pdf looks like page 5 indicates 1 Tach input that can take either type of signal

dave

[Roger S]

Hi Dave

Yes that is the very one, so on page 5 it shows a coil as I have, with a solid black line going to it from the TACH position on the control box plus an extended black dotted line going to an ECU/ECM Ignition Box (TACH OUTPUT).

As I do not have the ECU,does this then mean I am ok to run a new wire from the neg on the coil back to the control box ?

By the way I purchased the Dash from Classic Industries as direct replacement for the Rally dash, it sits behind the original fascia .Not sure this makes any difference as I expect the control box is universal.

Sorry electrics are not my strong point.

Many thanks

Rog

[Dave999]

from what i can tell

you plug in the wire from the coil negative to Tach in
and you configure the tach input on that adapter to one of 3 settings, you don't want 5 volt/ECU and you don't want BUS which is digging the tacho signal out of the ODBII connector on a modern car i.e CANBUS signal off of one of the pins in the connector hidden under the dash. You want the other one

the dotted line is there to indicate either type of signal

one direct from the coil negative or one from some kind of electronic source

should be in the setup menu on the screen of the main display under TACH. one presumes this involves lots of button pressing to scroll through a load of stuff you won't use before you get to the stuff you want to use much like programming your central heating.

Page 7 has it covered


Dave

[Roger S]

Hi Dave

Yes, there is a button to press which has to be mounted somewhere accessible and as you say lots of pressing to reach the programme you require.
Thank you very much for your time and effort, I will take a look at page 7 again. Will let you know how I get on, This weekends project.

Regards

Rog