2 hours ago, Emerald280Z said:

Wanted to revive this to see if you all can help me with my tach. Did 280ZX upgrade to my 280Z. Now it reads well at idle then if I blip to throttle it goes to 0. Eventually it goes up but bounces around. I’ve tried a new tach and it does the same. Using a FAST PS40 1.4ohm resistance coil with matchbox distributor. 

You might have luck with this:

 

https://www.technoversions.com/TachMatch.html

Just now, Racer X said:

You might have luck with this:

 

https://www.technoversions.com/TachMatch.html

First he needs to take out the TIU and 10K resistor to see if he has a problem. I would not be surprised if getting rid of those (along with ensuring the stock resistor is in place) fixes his problem.

Also, here is a picture of the resistor in the passenger footwell of my 260Z. As @Zed Head said, it's taped up like a mummy. It might have different connectors in the 280Z, but this should give you an idea of what you should be looking for. It will probably be below where the engine wiring harness comes through the firewall.

That's the original round style that they used on the 260Z's.  The 280Z's used the rectangular one like in the drawing you posted.  It looks just like the drawing.  It's folded over then taped up, so it's a different shape of lump.

I didn’t immediately see the stock resistor there as I quickly removed the TIU with my 3yr old in tow. 
 

Just removing the TIU made the tach work!  Is there a benefit or harm to removing the resistor I soldered in if the tech is working? 
 

Thanks again and happy I found this thread as FB responses months ago were not this helpful. 

1 hour ago, Emerald280Z said:

I didn’t immediately see the stock resistor there as I quickly removed the TIU with my 3yr old in tow. 
 

Just removing the TIU made the tach work!  Is there a benefit or harm to removing the resistor I soldered in if the tech is working? 
 

Thanks again and happy I found this thread as FB responses months ago were not this helpful. 

FB is good for posting pictures and getting lots of bad advice that buries the responses from the few knowledgeable people. 

that is the truth. happy i found this and thankful for the replies.  removed the resistor I put on by coil and all seems to be good.  running a smooth 850-900 idle

1 hour ago, Emerald280Z said:

that is the truth. happy i found this and thankful for the replies.  removed the resistor I put on by coil and all seems to be good.  running a smooth 850-900 idle

No fuss, no muss, no unsightly build-up. We are glad your Z is operating normally.  I would not be surprised if it drove better now.