Thanks for the pics. I'll dig through them when I get a chance. But I'm in agreement with crayZlair. I'm thinking that's not a cap at all.

What are the long slim rectangular things with a bunch of leads? Can you read the numbers on them? Dark maroon or brown things with seven leads or so?

56 minutes ago, Captain Obvious said:

 

What are the long slim rectangular things with a bunch of leads? Can you read the numbers on them? Dark maroon or brown things with seven leads or so?

Can't be sure w/o the proper schematic, but I believe these are what is typically called a PEC. Packaged Electronic Component. Custom designed mix of resistors/caps, etc. Designed to take less space on the circuit board.

3 hours ago, Captain Obvious said:

Thanks for the pics. I'll dig through them when I get a chance. But I'm in agreement with crayZlair. I'm thinking that's not a cap at all.

What are the long slim rectangular things with a bunch of leads? Can you read the numbers on them? Dark maroon or brown things with seven leads or so?

the one on the right side of the last image is `Hitachi FA8028-6G2` the one on the middle is `Hitachi FA8030--6H3`

I should have prefaced with some more information about the ignition system.

280z tach, 26061-AJ5000-81

Distributor - E12-80

Coil - MSD Blaster (Bypassed Ballast Resistor)

260z Transistor ignition unit removed

Last night i added a 2.2kOhm resistor to the wire that goes to from the tach to the coil, no change in the status, still dead from 0~1500.

The wiring is similar to https://forums.hybridz.org/topic/104933-1974-260z-with-e12-80-280zx-distributor-swap-wiring-with-tach-hook-up/

Could there be a way to bench test the tach? It would be nice to be able to replicate the voltage trigger on at the bench to see if it has been fixed, rather than installing it multiple times.

12 minutes ago, heyitsrama said:

I should have prefaced with some more information about the ignition system.

280z tach, 26061-AJ5000-81

Distributor - E12-80

Coil - MSD Blaster (Bypassed Ballast Resistor)

260z Transistor ignition unit removed

Last night i added a 2.2kOhm resistor to the wire that goes to from the tach to the coil, no change in the status, still dead from 0~1500.

 

So the tach needle just sits at zero, completely still, not even a quiver until engine RPM gets to about 1500, then it jumps up and sits steady at ~1500 and works normally/smoothly up to the high end?

Pretty sure that a 260Z already has the 2200 ohm resistor.  It looks different than the later models but it's there.  Since you have the tach out you could measure resistance back to the coil negative.

You could make three or four jumper extensions and run them out from the tach plug to wherever you want to set the tach for testing.  Still have to start the engine but not so tedious to run a test.

8 minutes ago, Zed Head said:

So the tach needle just sits at zero, completely still, not even a quiver until engine RPM gets to about 1500, then it jumps up and sits steady at ~1500 and works normally/smoothly up to the high end?

Pretty sure that a 260Z already has the 2200 ohm resistor.  It looks different than the later models but it's there.  Since you have the tach out you could measure resistance back to the coil negative.

You could make three or four jumper extensions and run them out from the tach plug to wherever you want to set the tach for testing.  Still have to start the engine but not so tedious to run a test.

Here is what it looked like yesterday, I'm going to go check the resistance in the wire to the coil.

 

https://www.youtube.com/watch?v=Ir33l7k_dCM&feature=youtu.be

You didn't show higher RPM like 3-4000.  But it looks like a physical problem might be a possibility.  Sticky needle maybe, something dragging on it.  Worth taking a close look at the needle movement itself.  Dust, crud, rust.

@Zed Head

2213ohm to from the tach to the coil.

Ill double check the movement of the needle.

I don't really know how tachs move the needle.  But I think the sweep of the needle is a continuous function, not a set of discrete steps.  I found a Google thing with a nice color drawing and some words.  Not sure if it's right.  But, digging in to what's supposed to make the needle move, the principles behind it, might offer a clue.

https://mechanics.stackexchange.com/questions/25584/how-does-the-tachometer-on-my-dashboard-actually-work

There is a slight bent at the end of the shaft that holds the needle, nothing that make its bind on the edges, but im trying to massage it back into place.

On a side note what is this component between the white and black wires? If you put a small flat driver form the bottom you can rotate the silver plate on the topside. 

 

 

 

Edit, it seems like a potentiometer, the far left is the ground, the bottom one is the vcc, and the top right one is the output.

Edited November 29, 20204 yr by heyitsrama

Looks like an adjustment.  I know that the voltmeter has a similar slot that I used to adjust the needle position.

Back to how it works.  The signal from the coil is just a voltage pulse.  The capacitor(s) just "collect" those pulses and convert them to some sort of steady voltage that creates a magnetic field.  More pulses equals stronger field.  So, what components fail in a way that makes them fail sporadically, to make the needle jump then fall back like yours does?  Sometimes they work and sometimes they don't.  I assume that there are diodes involved also.  

Not an electronics guy, just like to dig as deep as I can.  The above is a simpleton's guess at how the tach works.  Feel free to correct.

The needle movement is similar to what happens with a funky ignition module.  Is it possible that the problem is the ignition module and not the tachometer?  Your point about some sort of test bench is relevant.  I was watching Wheeler Dealer and the guy took a tach to a guy who had a pulse generator for testing them.  So they aren't that uncommon.