Rev counter

[Hugo]

I recently bought a Series 2 Roadster imported from S. Carolina. It is ALMOST in running order - some work been done - some still to do. When I turn on the ignition, the rev counter goes right round to maximum & stays there (with some fluctuations) when the engine is running. Can someone advise what drives the rev counter - there is nothing on the back of either camshaft? Does anybody know if this is likely to damage the instrument? Many thanks, Hugo Miller

[mark10337]

The white wire coming off the coil drives the rev counter. This feeds via the main loom into a 3 way connector located under the rev counter. This also has another white (unfused supply) and a green wire (fused supply) that connect to the 12V power on each terminal of fuse 7.

[mgcjag]

Hi Hugo....it helps if you have a wireing diagram...you can find one in the knowledge base section....justto add to what Mark has said the green is a 12v supp,y.....the rev counter works on impulses through the white wire which is just looped in the rev counter through a pickup..the white takes power when you turn the ignition on loopes it through the pickup then to the coil and distributor, so as the points make and break the pulses operete the counter......

[Riv944]

Hi Hugo
Had the same problem once on my series 2, it turned out to be a faulty rotor arm which was shorting to earth. Obviously the car wouldn't start either. I changed it out and the car started ok and the rev counter works fine. Check the rotor arm.
Hope this helps.

Ian

[Quattrofrank]

had almost the same issue, I solved it with putting a separate 12v to the green wire until I I fixed it. Previous owner had mixed up some wiring.

Try a 12v to the green wire first, if not check the white wire going to the coil

[Hugo]

Nothing's ever simple, is it? This is a LHD car with air-con, and it has a steering column ignition switch directly below the rev counter. So I can't even SEE the back of the rev counter with a mirror, let alone get at it. So I need to go in from the top or side I guess? I have hinged the centre panel down but that doesn't reveal much in the way of fasteners. One thing I can say is that it's not the rotor arm, as the engine starts & runs ok. Incidentally, there's a small electrical box just above the steering column lock, screwed to the underside of the panel above the ign switch. Any ideas what that might be?

[mark10337]

Not sure what that box is but it might be what you are looking for. The connector is usually around that area. Best way is to take the under dash cover of, lie on your back and look with a good torch. Should be a 3 way connector block - not dissimilar in looks to a relay mounting. This will have 2 white and 1 green wire.

[Hugo]

That's the problem - I can't see ANYTHING from underneath - I have the LHD steering column lock and the air-con in the wy. But in the meantime I've managed to get the lid off the dash & gone in that way - there is a 12v+ feed to the green wire when the ign is turned on. I guess that means it's the instrument itself. Not quite sure how I'm going to re-connect the demister pipes but that's another job for another day :)

[Hugo]

OK, next question; Who overhauls these instruments? And finally - if I fit a 123 ignition system, will that upset the rev counter?

[christopher storey]

Speedograph Richfield are good for all instruments. However , if you are going for electronic ignition , you will almost certainly need to change the internal circuitry of the tachometer as very largely these early electronic tachos don't work with modern electronic systems. There are plenty of threads on this on this board ( and also on the desirability or otherwise of e.g. 123 )

[Hugo]

Sorry to be a complete dummy, but being new to this forum I don't actually know how to research other posts on this topic?

[JagWaugh]

Hugo,

Just below the headlamp on the Picture at the top of the page you will find a search tab. Click on that and enter "123 RVI" or "123 tach" in the keywords field then hit enter, this will return a list of posts here on the forum with these keywords.

Andrew

[Gfhug]

Also search for "Spiyda"

[Mark Gordon]

Or, first check at the bottom of this thread under "Similar Topics."

[Hugo]

Ok, found my way through that lot - thanks for help with navigation! I had previously read a 'rave review' on here of the 123 system, so I thought that was the way to go. But after reading all the other stuff I'm not so sure. What are other members' experiences with the various systems? I wouldn't want to libel anybody, so if other members could just tell me what they would recommend that would be helpful. Incidentally, a while ago I had a very odd experience after I fitted one of the Simon BBC distributors to my wife's Morris Minor tourer. Basically, the car would not start - if you tried to crank it, it would kick back so violently it felt like it might break the crank. No matter how far I retarded the timing it did the same. It would start & run quite happily on the starting handle though. The only explanation I could think of for this odd behaviour was that the heavy current going to the starter motor (which is right next door) was triggering random sparks in the electronic stuff. Whether this was a fault in the starter I never found out. I have a reduction starter on there now but never got round to trying it with the SimonBBC distributor. I have to say SimonBBC were most helpful. They were as baffled as I was, and they sent me another new distributor F.O.C., but it was just the same. I seem to get all the weird stuff!

[JagWaugh]

I wasn't really convinced of the 123 when they first appeared. as they seemed to have some reliability issues at the beginning. I did make and fit quite a few "point saver" units over the years, and thought that these were about all that was needed if the distributor was in good condition.

About 4 years ago I started to change my mind. I've fitted 15 or so to various different cars, none of these has failed. The last 3 were 123/tune units. They cost a bit more than sending your dizzy off to distributordoctor.com for a full rebuild (Martin Jay does an excellent job), but for me the combination of being able to define and switch between two curves ("Race" and "Economy" for example) and also define a rev limit for each curve is worth the additional cost if you intend to loan or race your car, or if someone steals it and goes for a joyride.

I recently had the chance to compare a 123 against a new Alfa distributor using a Bosch Motortester - the wave form on the 123 was much better whichever aspect we examined. This car had had some modifications, so the owner wanted to be able to tune the curve, but wasn't willing to go to the expense of EDIS... yet (only time will tell).

I'm not really a big fan of upgrades, but the 123 is easily reversible, and adds some clear benefit for a reasonable cost. The only downside is that they are a bit "bling". Keep your old dizzy in working condition just in case.

[christopher storey]

I know others disagree, but my advice is unequivocal : avoid electronics. In the group of cars I work on , Jaguars mainly being XK150, Mark VII and several Es, including 2 of mine which are still on points , but also including my Daimler V8 and a Bentley Speed Six and 2 Derby Bentleys we have had failure after failure . I wonder whether our damp climate has something to do with it as experience seems to be better in the USA. I can only advise that if you must go electronic, make sure that a. it is reversible at the roadside and that b. you always carry points , condenser and any necessary wiring to revert back to points with you as a get you home measure