Why change the tach on upgrade?

[75Carrera]

OK. My sweet fresh 3.2 is in the car finally. We did figure out what the extra wires were for since I don't have a security system, air or need for the old fuel pump connection since we moved that up front. We kept the original fuel lines and oil lines but added a newer carrera oil cooler (looks like 24 or more brass tubes). In Marks descriptions he mentions keeping his original tach. Others have posted and I always understood the tach needed to be upgraded but don't know why or how since the connection appears a little different.

Who knows where I can find some pics and/or information about why and how to switch out the tach?

[Early_S_Man]

Donny,

Your tach should work fine. With earlier '69 - '70/'71 tachs that used a ballast unit ... the issue is the weaker signal level on the TD lead ... some tachs work, some don't.

Try yours, and maybe you won't have to change it out.