Tacho only working during cranking - 260z

[RAP260]

Howdy All,

So, rather than making anymore assumptions, I'll just ask. Googling myself in circles. 

Hardware : 1977 260z / Unilite Distributor / Mallory e-series coil

Details : Haven't had a functioning tacho for a few years, due to having a 6al controller. 6al died, so I've returned to the standard coil / distributor wiring setup.

So far, only connected black/white tacho wire to the coil positive. And as the title suggests, it's only working when its being supplied 12v. With the car running I can get it to work, by simply turning the key ( without engaging the starter). 

Looking for input. Is this a signalling or a tacho power supply issue?. Or am I supposed to something with the handful of other wires dangling under my bonnet... Lol

 

Cheers,

Rob 

 

 

[Enzo]

Hi Rob, I have a 1976 260z . The distributor black wire goes to the distributor neg (-) side.  The black/white wire goes to the Coil pos (+) side.  There should be a second B/W and G/W that went to the resistor but if you have bypassed that they should be joined together.

260z RHD wiring..docx

Edited August 18, 2020 by Enzo

[RAP260]

3 hours ago, Enzo said:

Hi Rob, I have a 1976 260z . The distributor black wire goes to the distributor neg (-) side.  The black/white wire goes to the Coil pos (+) side.  There should be a second B/W and G/W that went to the resistor but if you have bypassed that they should be joined together.

260z RHD wiring..docx 211.02 kB · 6 downloads

Cheers Enzo. 

Finally a running tacho again. 

Mine had an interesting side affect though. Had to use a ballast resistor between the BW and GW wires, otherwise the car won't stop. I can hear it powering the distributor when I connect them directly together. 

Unexpected behaviour? 

 

Edited August 18, 2020 by RAP260

[RAP260]

Ahh, my bad. In my head I interpreted BW as Blue/White, as I couldn't see another Black/White. 

After digging around I just found it. Buried under 40 years of tape... 

It's in the vicinity of the distributor. I'll give it a go and report back. 

[RAP260]

And we have a winner!! 

Thank you so much @Enzo

Thanks again, 

Rob 

[RAP260]

Ok... So after I've warmed the car up, I'm back to the same original situation. Tacho only working when the ignition is in the crank position, 12v supply. I let the car cool down for an hour, it ran for a short moment, then started fluttering and stopped again. 

Clearly there's an electrical connection issue. I've tried moving the harness around, with someone watching the tacho, and nothing. 

I need some insight here.

Looking at the schematic, the Green / White wire is supplying the running voltage (9v?) from the ignition switch? 

 

 

 

 

 

[AndBir]

9 hours ago, Enzo said:

The distributor black wire goes to the distributor neg (-) side.  The black/white wire goes to the Coil pos (+) side.  There should be a second B/W and G/W that went to the resistor but if you have bypassed that they should be joined together.

Likewise on a 74 260z.

I found the length of the wires to help along with the wires going to the coil were taped up together.

Not sure if this helps: 

[RAP260]

40 minutes ago, AndBir said:

Likewise on a 74 260z.

I found the length of the wires to help along with the wires going to the coil were taped up together.

Not sure if this helps: 

All input helps , thank you.

My connections are currently ...... Agricultural, to say the least. But should be functional, in my previous experience. I'll perfect everything, aesthetically, once the fundamentals are sorted. 

The Distributor "Black wire"??. Is this wire important?. As I'm not currently seeing it. 

 

 

Edited August 18, 2020 by RAP260

[RAP260]

So I now at least understand why the tacho works during cranking. The G/W wire provides power directly to the Tacho during cranking, from the ignition. The point of the B/W wire seems to be providing power during normal running?? 

On closer inspection the wire I thought was B/W was actually B/Y. Which probably explains my issue. 

I've decided to pull apart the wiring harness, in the engine bay. As I now suspect the original B/W has been replaced by the L/W. Which I had running the Tacho previously ( with a resistor ). This wire is clearly a different gauge / quality , but it has the thick plastic sleeve I've seen on pictures of the original B/W.