also Zed head that there is a 2.2k ohm resistor in the wire harness on the passenger side front kick panel where the oem 260z ignition module is located. I believe that is also for the tachometer circuit. I which I knew what voltage signal Nissan was looking for?

If it was mine I would measure resistance to ground through the blue wire that heads back to the tachometer.  Since you have disconnected the original TIU the tachometer should be the only thing on the circuit.  Not sure what it should be but it might show something.  Do it with the key on and off.

1 hour ago, kully 560 said:

what voltage was it designed to operate on?  

12 volts.  Power is supplied to the positive side of the coil, 12 volts, it passes through the coil and up the blue wire, through the 2.2 Kohm resistor and on to the tachometer.  As shown in the drawing.  The ignition module turns the 12 volts off and on.  That's what the tachometer is designed to see - a 12 volt off-on (aka square wave) signal.  The MSD tachometer wire (gray wire) is supposed to produce a square wave that looks like the one created by the ignition module.

Edited April 1, 20231 yr by Zed Head

30 minutes ago, Zed Head said:

If it was mine I would measure resistance to ground through the blue wire that heads back to the tachometer.  Since you have disconnected the original TIU the tachometer should be the only thing on the circuit.  Not sure what it should be but it might show something.  Do it with the key on and off.

12 volts.  Power is supplied to the positive side of the coil, 12 volts, it passes through the coil and up the blue wire, through the 2.2 Kohm resistor and on to the tachometer.  As shown in the drawing.  The ignition module turns the 12 volts off and on.  That's what the tachometer is designed to see - a 12 volt off-on (aka square wave) signal.  The MSD tachometer wire (gray wire) is supposed to produce a square wave that looks like the one created by the ignition module.

 

I do have the blue wire taped up neatly in the harness by the coil, but I can read it from the tachometer side. good idea, I do understand that the oem system and the msd are both square wave except the difference is the msd pulses at idle correct, which would still cause the tachometer to bounce at idle. maybe for the heck of it I will hook up the msd tach output directly to the tachometer and see what happens, all it can do is bounce I believe. thanks again

The MSD tach wire bypasses the multiple sparks.  That's the reason they have it on the MSD component.

Not sure what you mean by blue wire taped up by the coil.  How is the MSD tach wire connected to the tachometer?

If you could draw out your circuit and post it somebody might have some ideas.

Would the 12v in still be 12v after a 2.2KOhm resistor? Wouldn't it be lower?

yes, it should be lower with the resistor.

I did tape up the blue wire by the coil, and I did run a single wire from the msd tach output directly to the tachometer.

now if the msd bypasses the multiple spark output on the tach output connection, which I did not know it would be worth a try! 

1 hour ago, Patcon said:

Would the 12v in still be 12v after a 2.2KOhm resistor? Wouldn't it be lower?

It would depend on current flowing through the transistor, the one in the drawing (if that's what it is).  It's that meditation law.  Oooohhhmmm...

I tried the msd tach output wired directly with the tachometer and it does seem normal rpms and no bouncing at all. except when the cooling fan comes on, I do get a big dip on the tachometer. It must still need a resistor and not the technoversion v-booster. which all it is doing is raising the voltage signal and I am lowering it with the resistors. I have a 1watt resistor kit coming tomorrow from amazon and I will put the stock 2.2k ohm in line with the msd output connection and the tach input connection and see if that corrects the drop under current load. if not, I will have start testing different resistor values to see if I should be able to correct the drop.  thanks, everybody for the help! and Zed Head for the heads about the no pulse from the msd tach connection that was a good call.

Seems like what you really need to do is move the power supply source for the fan.  The tachometer and MSD aren't the source of the problem.  It's the power supply to the tachometer and/or the fan.