How to convert a 1969 tacho to work with a later car
Posted: Thu Dec 29, 2011 2:56 pm
I have been asked a few times about the 1969 tacho and will it work with a later car.
Well, yes, but it will need modifying.
In 1969, the 911 was equipped with a CDI and a small cylindrical tacho driver device. This sends a larger tach trigger pulse to the tacho.
In the later cars, the tach trigger is driven off the points, a nice 12V pulse that just isn't big enough to trigger the 1969 tacho.
To get around this, I change a resistor in the tacho to allow the smaller signal to trigger the tacho.
This will probably work with earlier, non CDI tacho's driven by a CDI, or MSD or similar.
This works on PCB's that look like this inside...
The resistor to be changed is the Orange White Orange one.
This is changed for a 6.8K Ohm 1/8th Watt.
See below
And here its is re assembled, and working.
Venture into modifications at your own risk. There are a multitude of different tacho's and ignitions systems. They are not all the same, and this modification may not work with all tacho.
Have fun
Tim
Well, yes, but it will need modifying.
In 1969, the 911 was equipped with a CDI and a small cylindrical tacho driver device. This sends a larger tach trigger pulse to the tacho.
In the later cars, the tach trigger is driven off the points, a nice 12V pulse that just isn't big enough to trigger the 1969 tacho.
To get around this, I change a resistor in the tacho to allow the smaller signal to trigger the tacho.
This will probably work with earlier, non CDI tacho's driven by a CDI, or MSD or similar.
This works on PCB's that look like this inside...
The resistor to be changed is the Orange White Orange one.
This is changed for a 6.8K Ohm 1/8th Watt.
See below
And here its is re assembled, and working.
Venture into modifications at your own risk. There are a multitude of different tacho's and ignitions systems. They are not all the same, and this modification may not work with all tacho.
Have fun
Tim