70 510 sss tachometer down

[Labubre]

Hi,

Do not exactly remember when it happened, but lost it. The needle won't move.

Park signal works, oil signal works, battery signal works too!

Before i start the engine -> first picture

Whit engine at idle -> second picture

 

I remember an electrical issue i had that brought my headlights (the stronest light) not to work anymore...i remember kinda smoke coming out the ignition switch keyhole!

 

Could those 2 issues be related?

Looking for advices to check and recover tachometer as i would not like to reach too often the 8k rpm! 😁

 

[datzenmike]

All the ignition switch does is power some of the fuses in the fuse box that need to be turned on/off with the key. If wipers, heater turn signals work then that part id working.

 

Where does the tach get it's power? Is it from the instrument cluster? Looks like everything is working so have a look how the tach is connected to the instrument cluster for loose connection. Included in this is the signal from the coil negative terminal. Check that the connections are secure.

 

The engine works so that signal end is working.

 

This leaves the tach itself. Maybe it has failed.

 

 

[iceman510]

The tach signal in a 510 is powered by the ignition pulses off the coil/ballast resistor with a separate harness.  The lights are from the cluster harness if i remember right. 

 

The harness from the coil to the tach should be checked.  There is also an induction loop wire on the back of the tach that harness connects to.   

[datzenmike]

The tach is inline between the coil negative and the distributor ground through the points. If the induction loop was broken the engine won't start. The tach in my 620 was the induction type from a 1200, though I think the actual 620 tach was not inductive but a single wire.. 

 

 

[ggzilla]

Yes its true, if the tachometer wire is broke or accidently got disconnected, or connections have gone bad, the car wont start

 

some important things to note are

* Inductive tachometer cannot short out the ignition as there is no direct connection

* if the tachometer has an internal fault, the engine keeps running

* Inductive tachometer can be wired multiple ways (either to coil POS side or coil NEG side) and work correctly

 

newer Datsun tachometers starting around 1974 have a single wire, the voltage-trigger wire. This kind of tach can short out the ignition

 

510s and early 1200 tachometers also have a single wire, the loop wire. Both ends of the wire are connected to the wiring harness. The harness has two wires, the tacho has only one signal wire, along with a 12V wire and several lamp wires. The loop is normally connected to coil + side via the factory harness. Although as many have discovered it also works from the negative side since it is only senses the current, the polarity doesn't matter

 

The factory installation PDF is inked to in this discussion

Re: Factory tach wiring

Quote

Post by Byron510 » 09 Jul 2013 23:47

As explain in Rob's post above, the tach pick up is actually to the + side of the coil. It's and inductive pick up, meaning there is no actual connection, but senses a voltage spike just like a timing light works on your plug wires.

[datzenmike]

As far as the 620, 720 and 810 single wire go, the FSM has the tach wired to the coil negative side. Might work on the positive side just no need to try it.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

[Labubre]

Hi

Pull this one aside as was not a big deal and also was more focussed on my headlight issue.

Pulled the tacho out to have a look at wiring: i have 2 whites wires with bullet connectors leading to a Black/Green wire and a Black/Blue wire.

On Coil side i have a small black wire from "+" to balast "+". 

Black/Blue wire connected to the Balast "-"

Black/Green wire not connected...

Also have a Black/White wire connected to coil "+".

Obviously, during re-installation, something went wrong.

From what i read, i wonder if both Black/Green and Black/Blue should not be connected between coil "+" and balast. 

And this Black/White wire connected to Balast "-".

 

Does it sound correct?

Looking for confirmation OR better fit!

Thx

 

 

[ggzilla]

19 minutes ago, Labubre said:

Black/Green wire not connected...

That would explain it. It should be connected to Ballast +

 

The two wires connected to Ballast -:

* Coil +

* IGN-START

[Labubre]

Thanks for reply ggzilla

After a try and before reading you i did a test and right now my coil/balast are connected like this:

Balast + to Coil + with a short black wire

Have the Black/Blue wire (IGN SWITCH) connected to Balast +

Have the Black/White wire connected to Balast -

The Black/Green wire connected to Coil + or not connected at all...The results is the same, engines fires up but TACHO is still not operating.

Pretty much like on this picture

 

 

So ggzilla, if i follow you, i should invert the balast in my wiring...i was not expecting polarity to be a concern with "ballast resistor"

Will try...

 

"HEADACHE ALARM"

Also found some documentation about the "inductive white loop" behing the TACHO...those white wires need to be pulled out to engine compartiment be installed in serie between +12V from ignition switch & the ballast resistor...

My 2 white wires are bullet connected to Black/Blue & Black/Green....and those 2 are heading out of the harness with the Black/White. As i found on the SSS wiring diagram below (oh, yes my 510 is a SSS)

I do believe my tach used to work before we pulled out the engine.

But there are no such kind of wiring available and ready to be plug back in!!!

 

Perhaps i am "lost in translation" and need a datsuntory whisky! 6.21pm here...

 

 

 

 

 

 

 

[Labubre]

Hi

 

RESET OCTOBER 25

Perhaps should have started with this

 

BEHIND MY TACH, 4 CONNECTIONS

- Black wire = ground

- Green wire = +12V from IGN SWITCH

- white wire connected through bullet to a BLACK/GREEN stripe wire

- white wire connected through bullet to a BLACK/BLUE stripe wire

DOES THAT LOOK CORRECT?

 

HARNESS AROUND COIL LOOKS LIKE THAT

- BLACK/GREEN stripe wire that is not connected as of today. Is it the one from the TACH?

- BLACK/WHITE stripe wire connected to BALAST "-"

- BLACK/BLUE stripe wire connected to COIL "+". Is this the one from the TACH?

- BLACK wire that is connected to COIL "-"

DOES THAT LOOK CORRECT TOO.

 

This engines fires up, but NO TACH.

 

Is something missing here to get the TACH working?

Thanks

Seb

 

 

 

 

[ggzilla]

POLARITY

* as can be seen from the JDM documentation, the loop wire connects inline with coil feed POSITIVE wire. This is the factory configuration

* as @datzenmike loves to say, it also works with custom wiring inline with coil NEGATIVE wire

 

As the tachometer triggers off the current pulses it doesn't matter about polarity. The wiring is much shorter and simpler when using the dashboard positive wiring, as compare to longer wires if you run custom wires out to the coil and back

[ggzilla]

On 7/26/2025 at 9:21 AM, Labubre said:

I do believe my tach used to work before we pulled out the engine.

Ah, yes. Most likely a connection was forgotten. It all depends ... on how your car was wired. Here in USA, tachometers are fairly rare, and many have custom wiring, or even modified tachometers

[ggzilla]

2 hours ago, Labubre said:

HARNESS AROUND COIL LOOKS LIKE THAT

- BLACK/GREEN stripe wire that is not connected as of today. Is it the one from the TACH?

- BLACK/WHITE stripe wire connected to BALAST "-"

- BLACK/BLUE stripe wire connected to COIL "+". Is this the one from the TACH?

Now to the COIL

Polarity makes a subtle difference to the COIL. For best performance and long-term reliability, the coil should be connected correctly, although it does work either way

 

* Black/white is the coil feed POSITIVE wire which connects to one side of ballast resistor

* The other side of ballast resistor has two wires: Black/green (which goes to coil POSITIVE) and 12V from ignition START (has 12V only when key is turned to START)

 

After this if the tachometer does not, is your tachometer using the factory under-dash tachometer wiring harness? or custom wiring harness? Has the tachometer been modified? And what was the wiring when it worked, before the engine removal?

[Labubre]

[Labubre]

Standard TACHO here

I believe it used to work but i am not 100% as short time after getting the car, the engine rebuilt started

 

COIL "+" and BALAST "+" are connected by a short black wire. 

On COIL "+", i have the Black/Blue wire that goes to IGN SWITCH.

I also tried to connect the Black/Green wire to COIL "+" and the engine was able to start as well. Meaning small black wire, black/blue and black/green connected on same connector.

Turning the engine ON, I saw the TACHO needle bump a little but not significant i guess.

 

Thanks anyway for your support!