1971 240Z Tach Question

[twoforty z]

Hey all.

 

Ive had to rewire my dash due to previous owner doing some interesting wiring.

Quick question as ive put it all back in and my tach doesnt work (ignition coil loop style thingy)

 

Will a 1971 240z run without the tach plugged in? As ive heard they wont as the tach is wired into the ignition. Because mine does run without the tach plugged in.

Cheers

[d3c0y]

Do you have a later model electronic distributor in the car? If so the 240Z tach won't work anyway and is probably why it still runs ok.

[twoforty z]

No original points distributor and original induction loop style tach wired to positive side of coil

[d3c0y]

If you bridge the terminals on the tacho plug it will run ok without the tacho installed.

[twoforty z]

Without the tach plugged in and without the coil wires bridged my car runs.

So it appears its not wired in series as it should be.

Dash will come out again tonight and ill have a look.

I have 2 black/white wires at the coil and 1 green and white.

Green and white goes to resistor and both black and white go to + on coil. 1 appears to be straight from ignition other appears to go to tach.

My cars wiring is a mess, slowly fixing issues

[d3c0y]

Yeah get a wiring diagram and for this one look up the diagrams for the electronic ignition upgrade threads because they will tell you where the wires should go.

[twoforty z]

Ok going to bring this back up because im going insane.

 

My 1971 tach does not work. Period.

 

Tach is looped through ignition, power from ignition switch (black white wire) loops through tach and then to + of coil.

 

Tach has good 12v source and good earth

 

2x black/white wires at + of coil, both from same ignitiom power source, 1 is looped through tach, 1 is not. Both get 14v when running. Car will run when both plugged in or just 1 or the other.

 

1x green/white wire bypasses balist resitor for start up

 

Have tried 2 different coils and 2 different tachs. Same result. Nothing

 

Its a points distributor, all pretty much stock except 280zx alternator

 

Any suggestions? What have i missed?

[GregTas]

On the +ve side of coil I would have expected only the one wire that loops through the back of the tach. I looked on a diagram and it only showed the one B/W wire.

 

With another +ve wire on the coil the tach will not see the switching because it's effectively bypassed.

 

What happens if you just have the B/W wire that loops through the tach on the coil +ve?

[GregTas]

Here's a diagram. I chopped up the full diagram so it was a bit easier to follow.

 

Edited December 30, 2017 by GregTas

[krizza]

Hi Greg,

 

The way you currently have the wiring on your car is incorrect. The only wire that should be on the coil +ve is the b/w that goes to the tach. The g/w goes on the coil side of the ballast to give it full 12v on startup and will only show 12v during cranking. Once the key is in the run position the other b/w wire will be supplying 12v and should be on the opposite side of the ballast resistor to the coil so the coil only sees 9v during running.

 

Hope this helps you get your tach going

[GregTas]

Krizza, I'm assuming you meant your comment for 'twoforty z'

 

Looks like we are both in agreement on the likely cause i,e, the second wire on the +ve side of the coil.

Edited December 31, 2017 by GregTas

[twoforty z]

They 12v i measured is before the resistor, not after.

 

If i disconnect the 2nd b/w wire and use only the one that comes from the tach my car will still run but tach will still not work

[twoforty z]

Also i believe both black and white wires are factory fitted as they both run through separate fittings that plug into the dash harness and both look original

[krizza]

Krizza, I'm assuming you meant your comment for 'twoforty z'

 

Looks like we are both in agreement on the likely cause i,e, the second wire on the +ve side of the coil.

Sorry Greg, you are right I was responding to twoforty z.

 

Twoforty z, all of the wires you described are factory fitted and need to be wired as per the diagram Greg posted above. Both b/w wires connected to the coil will not provide the correct signal through the tach for it to work.

 

Of course the other potential issue once the wiring is put back in the correct order is that the tach may be bad. These induction loop tachs seem to be pretty flakey. The original in my car was intermittently faulty when I bought it, and a replacement I bought off the forum was DOA too. I had my original rebuilt with a new Smiths board to get it working reliably.

[twoforty z]

Well ive tried 2 different tachs both same result. No guarantee these tachs were working when i bought them.

 

Ive ordered a 280z tach that is triggered from the - of the coil so "should" solve my problem but id like to know why these tachs arent working.

 

Would dwell angle or breaker point gaps have any effect of the signal through the tach? These are 2 things i havent checked yet

[krizza]

I dont think point gap or dwell angle will have any effect on the tach.

 

The 280z tach is a much better option imo, because you can get it to work with electronic ignition systems and cdi boxes. Sounds like that is the way to go.

[aircobra]

there's a place in melb that fixes and test these

[Roady]

twoforty z - I had a similar problem. I had everything in the car and it was all working fine then one day it just stopped. It would no longer indicate past 4000rpm. The engine was still going past but the tach just seemed to hit a wall and wouldn't go past it. Swapped tach' same problem. Sent tach away to be tested and nothing wrong with it.

I figured there was a power drain somewhere so I systematically swapped and changed everything associated with the loop wire (swapping coils and several other things which I can't remember) but it didn't have any effect.

Took it to an auto electrician who couldn't solve it, so I gave up and did what you propose and put in a 280z tach interior into a 240z tach body , no dramas since then. Sorry I can't give you any other ideas to try

Edited January 1, 2018 by Roady

[twoforty z]

So the 280z tach arrived. Bit of rust on the face but internals looked good.

So i now have "Frankentacho"

240z housing

280z internals

260z face

240z needle.

And it works!

 

Fyi, 240z, 260z and 280z tach faces are all different. The spacing on 240z's is different to 260z's and 280z's "yellow" line at 6000rpm not 6500rpm but the spacing is the same as the 260z.

And the 240z font is very very slightly smaller