Tach Wiring.

[73 240Z Man]

My MSD recently died on my 73 240z so I eliminated it along with all the after market wiring. Now the Tach does not work. All of the stock wiring seems to be in place but I dont know which to connect to where (positive or negative side of the coil) to get the Tach to work. Any ideas?

The Z runs great w/o the MSD by the way.

Chris

[alhbln]

In the stock points/three wire tach setup, the tach is wired to the negative terminal of the coil. You will also need to remove the tach converter, which was part of the MSD setup to drive the original three wire tach.

[73 240Z Man]

Thanks for your reply. Do you know which wire it is? and what is the tach converter?

[alhbln]

The tach adapter would have been connected to the spade plug on the left side of the MSD 6A and the tach input. Could you check what was wired to the spade plug?

[ZCCOR#109]

I think your MSD may have had a module that attaches to the rear of the tach in place of the original wire loop.

Look at the back of the tach to see what the situation is. Remove the two wing nuts that hold the tach in the dash. do that by reaching around and up under the dash from the right side of the steering wheel. Ease the tach out of the hole and if there is resistence it may be a wire is holding it up. look for non standard ties or tape holding those wires.

the tach will only come out about an inch and 1/2 clear of the front of the dash so you have to tilt the tach to the right side to see the rear. The stock tach set up has a white wire going to the tach that is made into a loop through a small clear plastic cube. That cube has a hole in it that the small stud from the tach goes through. Covering the plastic cube and held on with a very small nut is a "U" shaped piece of sheet steel. The "U" goes into two slots in the rear of the tach.

If there has been an after market item attached there for the MSD etc. then it has to be removed and the orginal loop installed.

Good luck

[alhbln]

Lowell, Chris has the newer 'three wire' tach in his '73 240Z, not the 'four wire' current triggered tach with the white loop we have in our '72 model. The adapter could still be mounted behind the tach, good input!

[73 240Z Man]

I put in the MSD. Although it was years ago, I am sure I didn't put anything behind the tach. It connected through the stock wiring. There are a total of 4 wires coming out of the stock wiring loom at the coil. They are as follows.

1. Black/White stripe wire connected to the positive side of the coil.

2. Green/Yellow stripe wire connected to block under coil. (nothing connectied to the other side of the block which I believe is due to the pertronix)

3. Black/Yellow wire (not connected)

4. Black wire (not connected)

The coil also has 4 wires connected as follows;

1. Red wire connected to the positive side of the coil running to the pertronix

2. Black wire connected to the negative side of the coil running to the pertronix

3. Blue wire connected to the positive side running to the ballast resistor

4. Black/White wire connected to the positive side of the coil coming from the stock wiring loom.

*See attached pictures*

I should add that there is a wire coming out of the distributor about 3 inches which I believe was for the condenser which I don't need now that I have the pertronix.

Edited March 27, 2010 by 73 240Z Man

[alhbln]

Did you use the Pertronix to trigger the MSD or was the Pertronix Ignitor installed after you removed the MSD?

My guess would be that the green/yellow (sure it is green/yellow, not green/white?) wire runs to the tach, the block is the old ballast resistor.

If possible, could you take a photo of the back of your tach so we can compare the wire colors? See the post from ZCCOR#109 above describing how to remove the tach.

The black/yellow wire was wired to the throttle opener vacuum control solenoid, which has probably been removed on your car. The black wire was the original connection to the distributor points contact.

Edited March 28, 2010 by alhbln

[73 240Z Man]

I installed the pertronix and removed the MSD at the same time. And the green/yellow could very well be green/faded-37 year old-white.. It is possible to remove the tach but I just had abdominal surgery and will be layed up for about a month...

Thanks for identifying the other two wires...

If I understand you correctly, I can remove that block, right? If the green/ylw Or white wire is the tach wire, I connect that to the negative side of the coil, right?

Thanks for your help...

Chris

[alhbln]

Correct, you can remove the block and the green and yellow/white wire should be connect to the negative side of the coil.

Get well soon!

[73 240Z Man]

Thanks a bunch. I will give that a shot.. And thank you, I am gradually feeling better.

[73 240Z Man]

Alright, I tried connecting the green/ylw (or wht) wire to the neg side of the coil and the car wouldn't start. Plus when I disconnected the jumper wire it was hot. The car started fine without the wire connected and after it was running I reconnected it and the tach still didn't work. Now I am back where I started.

Any Ideas?