Tachometer wiring check

[minorissues135]

Hi, after many weeks of messing about replacing my rear axle casing, I'm finally ready to re attach my tachometer wires. I had a breakdown about a year ago now, finally, after much wrangling found a mismatch between the module and the coil as fitted to the car when I purchased it. To simplify things I took the tacho wires off, and now want to put them back on. The red wire from the ignition module is very long, not sure why? This goes to the coil positive and was wound around another wire also heading to the coil. The black wire from the module changed colour, went up to the tachometer, changed to brown/green and back down to the neg side of coil. Other wires on the coil

IMG_5154a.jpg (1.36 MiB) Viewed 161 times

are power and a radio suppressor. The tachometer worked fine like this, but before I reassemble, just want to check if this makes sense? I've looked at the Smith's Gentleman's guide, but as the back of the tach is hard to access, I don't know what model it is. Here's a photo of the set up as before...

[geoberni]

I'm not by any means knowledgeable about aftermarket Tachometer installation, I've never had one, but that Red wire which is presumably power worries me.
As an electrical engineer, I dislike cables wound around other cables like that, it's creating an electromagnetic field; probably too small to interfere with anything, but still not good practice. Cables should run parallel to each other.

[minorissues135]

That's partly why I'm posting the question. The red wire is longer though they might have simply cut the black wire down. I could cut it down to proper length to suit the distance between module and coil? Is there another solution without cutting it that would be preferable?

[minorissues135]

Thinking about induction, though the effect might be slight, the wire wrapped around the other will induce and be induced into current flow. I guess this might either feed back to the module, if it's sensitive enough, or confuse the signal going to the coil. Either way, it's not ideal I would think. for now, I think I might coil it separately, see the tachometer is still working, and consider cutting it to the correct length.

[myoldjalopy]

Yes, I would cut the red wire and fit a new connector. Just don't cut it too short!

[chrischris59]

What do you mean my module? I haven't come across a tacho module but know that it's a common fault for tachometers to stop working when ignition modules are fitted. years of playing with MGBs.

[minorissues135]

By module I mean the ignition sensor

[chrischris59]

Sounds like you have electronic ignition fitted. If you have a smiths tacho gauge fitted and in tiny writing at the bottom printed is RVI then its a compatibility problem. But RVC is a wiring problem.

[minorissues135]

Hi Chrischris, yes and when last tried the tacho was working fine, but I disconnected due to a breakdown, initially thought to be caused by coil failure. That turned out to be failure of the ignition sensor/module and on further investigation, failure possibly due to incompatibility between sensor fitted and the coil. New compatible sensor and coil fitted and when last run, the engine was a lot better. Just wanted to run it by people here in terms of the wiring.