Coil wiring

[Gfhug]

The S2 wiring diagram shows a white wire from the tacho going to the positive terminal of the coil then the white/black going from the coil negative to the distributor.
Mine has always had the tacho wire (now from an rvc converted tacho) going to the coil positive and the white/black coming from the same positive terminal to the distributor. Then there’s a black wire from the coil negative to earth, which isn’t shown in the diagram. The wires all look original.
It works, but when checking things prior to trying a 123 dizzy there is no 12 volts at the coil positive.
I shall admit to being a bit confused by this and will be grateful for any thoughts.

Geoff

[Tom W]

Does your car have a ballast resistor?

[mgcjag]

Hi Geoff...your coil cant have one side permanently earthed...you would never start the car...if your installing a 123 i would also suggest that you power it (12v) from the fuse panel and not from the coil as the 123 diagram suggests as there havd been problems with 123,s. powered from the coil......Steve

[Gfhug]

Tom, thank you, I should have said no ballast resistor
Steve, I know it all sounds silly but that is how it has been all the past six years. But your comment about powering the 123 from a separate source and not the coil will be followed, thanks

Geoff

[mgcjag]

Hi Geoff.....it just wont work with a permenant earth on the coil.....trace all your wireing again......your description of how its wired must be wrong....Steve

[flatfloor 3.8]

Hi what problems arise from wiring a 123 from the coil. Thank you

[mgcjag]

Dont know the specifics.....lots here on the forum and other forums....so better to be on the safe side and not take you 12v from the coil....Steve

[Tom W]

My 123 worked fine from the coil. It’s the RVI rev counter on the series 2 that doesn’t always work when the 123 is powered via the coil live.

[mgcjag]

Hi Tom...yes thats it.....knew there could be a problem couldnt remember what it was...thanks..Steve

[ALAN COCHRANE]

Geoff

It's sounds like your coil is wired in reverse. It would still work but the spark wouldn't be quite so strong. You will probably find that the coil negative terminal will have 12V applied. Although you say that the black wire from there connects to earth, is this actually the case or does it run at 12V?
I've checked my GT6 wiring diagram and the electronic tacho has a feed from the negative side of the coil, so with your setup it would be connected to the positive side, which appears to be the case.

Cheers

Alan

[Gfhug]

Alan, you were right, thank you
Steve, as always thank you for your wise counsel

123 set up and fired up first time
Now to find out why the (rvc) tacho isn’t working, but that seems to be a known problem and searching the forum later should help.

Edited to add: tacho now working

Thanks as always to the forum members for their help, guidance and being such good eggs

Geoff

Postscript: took the car out for a brief drive and the 123 was smooth on curve zero (the older 123 with 16 pre-programmed curves)

[abowie]

Edited to add: tacho now working

Thanks as always to the forum members for their help, guidance and being such good eggs

Geoff

Glad to hear it all works.

For posterity and my own interest how did you get the RVC tacho to work properly?

Might save someone else some time in the future.

[Gfhug]

Andrew, it was the same wiring mistake where the coil pos and neg had been the wrong way round. I put the rvc tacho pick up back on the positive side, but it should have been the negative terminal. The Spiyda website gave the correction pick up info.

Geoff