Factory Tach not workIng right

[GetX'd]

I have a 68 GTX with a factory tach along with the other standard gauges. I had the whole instrument panel refreshed and the gauges re calibrated. I then put in an MSD Ready to Run electronic ignition. This was all done at different times and then eventually installed. I had a new wiring harness purchased from Summit to wire the engine. Now everything is coming together kind of.....

the engine runs fine and the motor was dyno tuned and everything Seemed to run well (motor was not in the car). Engine went in the car and it still runs well although not road tested - but the gauges cut in and out. Like the tach will run fine one minute then not bounce at all the next. I can't tell so much on the speedometer, gas and temp cause I haven't had the car on the road.

what Do you all think about the tach cutting in and out? Like I said it works fine sometimes but not others. I'm a little stumped.....

 

[kiwigtx]

If the tach is a factory type, you will need an MSD Tach Adapter. This will convert the signal output from the Ignition unit to make it readable by the tach. Easy to wire in and should not take long to install. Summit sell these items. :icon_thumright:

 

[Icecobra]

On the ready to run distributor did you use the grey wire that is the output for tach? Did you use the - on the coil? I have found the - on the coil works best...

 

[GetX'd]

Icecobra - we tried as you suggested above to go to the negative of the coil. No impact. Kiwi also suggested an MSD tach adapter. That's a good solution but the distributor I have is a all in one ready to run - so it doesn't use and ignition box, therefore the tach adapter isn't applicable for my series distributor according to MSD.

Now the distributor is bouncing at all. Not even intermittently working. Anyone else have any ideas? It may be just that the tach - or wires are bad. I had all the gauges repainted and rebuilt several years ago before the motor was done and in thE car.

Not it sure what to do. Anyone have any ideas of things I can try to know for sure if the tach is bad or not? I hate to have to take those gauges out again. Electrical is simply over my head.

All replies are are greatly appreciated.

 

[kiwigtx]

Sent you a PM with the Instruction sheet link.