Factory Tach Size?

JMSII

Anybody happen to know the size of a CJ7 factory tach? Specifically the size of the dash opening. I am running an MSD 6 box, wires, distributor and coil and am having a hell of a time getting the factory tach to work. I purchased MSD's "tach adaptor" but I guess I am too stupid to make it work. MSD said that all Auto Meter tachs just plug into the recepticle on the side of the box. Anybody know the size off the top of their head? Thanks!

ironman_gq

I think its around 2 1/2 but im not sure.

dwloop

JMSII wrote
Anybody happen to know the size of a CJ7 factory tach? Specifically the size of the dash opening. I am running an MSD 6 box, wires, distributor and coil and am having a hell of a time getting the factory tach to work.

I purchased MSD's "tach adaptor" but I guess I am too stupid to make it work.

MSD said that all Auto Meter tachs just plug into the recepticle on the side of the box.

Anybody know the size off the top of their head?

Thanks!

I guess that makes two of us. I installed a MSD 6A and cannot get the CJ5 factory tach to work in any way. 🙁: Is the aftermarket tachs the only way to go?? :razz:

Thanks,
Dave

AMX69PHATTY

I don't have a Jeep, but the MSD & stock Tach in my '69 AMX works
with MSD 6T white wire triggered and stock Delco dizzy with a UniLite Conversion.
Do you have the MSD Instructions ?
They talk about two different kinds of Tach, Current Triggered and Voltage Triggered.
Also is the MSD White Wire Triggered or Magnetic Connector Triggered ?
Only if using the MSD Magnetic Trigger and a Current Triggered Tach
then the MSD Tach Adaptor is needed

Current Triggered Tach - two wire cinnections at Tach -
from Positive Battery post to ignition switch to Tach to Coil Positive

Voltage Triggered Tach - three wire connections at Tach -
from Positive Battery post to ignition switch to Tach to Coil Negative.
Coil Positive wire is split off beween Ignition Switch and Tach.
Third wire on Tach is attached to ground.

dwloop

I would assume from that description that the CJ factory tach was current triggered then. It has two wires, and was originally in series from the ignition switch to the power on the ignition module. Had to take it out of the circuit to install the MSD. In my install I used a Motorcraft dizzy and the adapter from MSD to user the magnetic trigger. So much better than the prestolite crap it had before! The reason for the magnetic trigger was because I eliminated the module. In reading your explanation, I need to connect one lead of the tach to switched power, and the second to tach terminal on the MSD? Or I need and tach adapter? EDIT: just re-read your post and answered my own question, I need the adapter... :oops: Thanks, Dave

76jeep

Ihave one in front of me and i am getting about 2 3/4 hole. It is out of a mid 70's cj5 or a cj7.

dwloop

As an update, the only I got the tach to work with the MSD was to replace it. Omix-Ada makes a replacement that looks very close to the original and works out of the box with the MSD 6A. I bought it on eBay for around $60. Dave

JMSII

So, did the replacement tach just plug in or did you need to use the MSD tach adaptor?

dwloop

The replacement from Omix-Ada is triggered directly from the tach connection on the MSD, no adapter... Dave