Hi, all. I just bought a 1973 240z from original owner, and he rarely drove it. That's good and bad. I'm sorting through the bad....

I have lots of questions that I'll post under separate topics. 

I have a simple question to start...

The tachometer isn't working. It's the old current measuring kind. He gave me a used one he bought, but it doesn't work either. He did get the ignition on the column changed at some point in the past. I'm trying to diagnose. Should the car still start if I unplug the tach from the the wiring harness?

 

Thanks! 

Edited April 25, 20204 yr by Dadsun
Clarify

Congrats, and welcome to the forum.  Yes you can unplug the tach and it will still run, in fact you can remove the entire dash and all the instruments she'll keep running.  It looks very nice, how many miles on the clock?

79K miles. And less than 6K in the last 17 years so it's sat a lot. 

It's a pearl white which I don't think is the original Kilimanjaro white. This picture shows  the original interior/exterior color scheme that I'd like to eventually get it back to. 

 

Thanks for the tip. I guess I'll try to measure the current on the white loop line on the wiring harness to see if the tach is being fed a current?

Are those stock colors for exterior and interior. I love it. 

Yes, but mine doesn't look anywhere near that good right now! Just what I aspire to. 

ZtooZ,.are you the one I saw on another thread who has spare working 240z tachometers? :-) (Saw in an old thread)

I do. Send me a photo and I will send you one to try. 
dpappe@gmail.com

With 7tooZ's help I corrected some wiring at the ignition coil and resistor, and now the tach works! Much appreciated! Even my spare tach works. 

I did notice when the car was running and I swapped one tach for the other that the car died as soon as I unplugged the tach's wiring harness. Is that to be expected?

Here is a pic of the current wiring under the hood that got it working. 

1 hour ago, Dadsun said:

when the car was running and I swapped one tach for the other that the car died as soon as I unplugged the tach's wiring harness. Is that to be expected?

Yes, that is to be expected for the early years.

59 minutes ago, Dadsun said:

I did notice when the car was running and I swapped one tach for the other that the car died as soon as I unplugged the tach's wiring harness. Is that to be expected?

 

2 minutes ago, Captain Obvious said:

Yes, that is to be expected for the early years.

When I was working on my 70/240z I drove for weeks without a tach and that is what my previous statement was based on.  The tach is picking up the signal and converting it to a visual aid, how can it prevent the engine from starting?

20 minutes ago, grannyknot said:

The tach is picking up the signal and converting it to a visual aid, how can it prevent the engine from starting?

Because on the early years they run the primary side of the ignition coil signal through the tach to provide pulses. That's the looped wire on the back of the "current sensing" tach.

Now, it would be easy to bypass that and get the ignition to work without the tach, but if everything is wired according to stock, it shouldn't run without a tach installed:

 

That said, however, I've not owned an early one either. I'm going off pics and documentation.

Like that can never be wrong...  

By the time they got to anything I ever delved deep into, they had switched over to the newer voltage sensing tach. I believe that was 74.

@grannyknot

were you running a stock distributor and ignition system? The earlier Z wire diagram would indicate that with the ignition key is in the run position there  would be no power to the POS side of the coil. After market ignitions like Pertonix  might change that. Just a thought.