Lotus Elan

Revcounter connection.

PostPost by: vincereynard » Thu Aug 31, 2017 10:52 am

The revcounter has a yellow wire and a red wire. The connections are white and white/black.

Any idea which goes where?

screenshot-from-2017-08-31-11-38-30.png and


Helpfully, the manual just shows 2 white?
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PostPost by: Foxie » Thu Aug 31, 2017 1:05 pm

I replaced the original tacho in my Plus 2 with a modern 'electronic' type.

The earlier type of tachometer shown in the workshop manual had the ignition supply to the coil looped through the tacho, which was driven by the current pulse.

The later type 'electronic' tacho is driven by a voltage pulse from negative side the coil, and requires a return wire to be fitted for this purpose.

You need to establish which type of tacho you have.

If it is the old type, there will be a continuous input and output. Check this with a test lamp

If it is the new type, the red wire would be connected to the positive supply from the ignition/ fuse 3 towards the rear of the centre fuse box, most probably the white cable, check this out. The existing white ( + supply) would still be connected to the coil, but also connected to the black and white wire to take the supply on to the coil.

The yellow would be connected to the signal from the coil.

The tacho will need an earth connection, either a terminal or an earth tag on the casing or clamping bracket.

Check everything !

Hope this helps :)
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PostPost by: mbell » Thu Aug 31, 2017 5:36 pm

A couple of images from my car, as when removing to do rvi to rvc conversion. Not the best but might help.
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20170817_135230.jpg and
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PostPost by: Foxie » Thu Aug 31, 2017 6:33 pm

It's hard to make out, but are there two connections to the right of the heavy green cable ( which is power in ) ? If so, it looks like the original current operated type. Mine looks identical, but it the case is original, the internal were changed, and has only the main power, signal, and earth connections.

Any chance of a pic from the other side ?
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PostPost by: bob_rich » Thu Aug 31, 2017 6:52 pm

Hi Vince

the two whites suggest that you have a current loop tacho RVI. The tacho should have two white wire coming out of the back and this should go to your white and white/black.

I assume your car is running and is -ve earth and the taco is OK. If so connect up the whites to the white and white /black. Then add an earth to the Tacho body. and take a separate lead form a +12V point to the 12V input on the tacho. If the tacho does not work try swapping the white and white black over ( so the current goes through the loop the other way) . You also need to find out what the red and yellow wires do. Suspect the are 12V input and the instrument regulator 12V input BUT this is a guess! as the colours are not as I have them on my diagram

I have taken a picture from my rebuild and annoyed it with the connections which may help in confirming the taco is an RVI and the connections

Hope this helps Best of luck

Bob
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PostPost by: mbell » Thu Aug 31, 2017 7:34 pm

Foxie wrote:It's hard to make out, but are there two connections to the right of the heavy green cable ( which is power in ) ? If so, it looks like the original current operated type. Mine looks identical, but it the case is original, the internal were changed, and has only the main power, signal, and earth connections.

Any chance of a pic from the other side ?


Yes this was RVI when I took the photo, it's now RVC and not back in the car so can't take any more pictures.
The two white cables for tach loop, there are male/female so shouldn't be able to get them backwards. One is power in, the other should go to the coil +12v.

Green wire is switch 12v power, black is earth to case. Lower partially removed bulb with Brown/Yellow and green wire is the alternator light i believe. There there full beam light with wires hidden, then red/yellow(?) to bulb is illumination.

Going back to Vince's original questions. The Red and yellow wire aren't original so you need to do some testing. I'd guess your tacho has been converted to RVC, so I'd agree with Foxie on likely one being 12v supply to coil (possibly connect to a white wire behind dash) and one being coil negative connection for the tacho. So I'd start by testing for 12v on them switched by the ignition, then check to see if either is connected down to the coil.
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PostPost by: vincereynard » Thu Aug 31, 2017 8:51 pm

As usual thank you all for your response and input.

I found a small label on the back of the tach. from Speedy Cables with a date of Sept 2010.
I assume that means it is a later electronic replacement.

A diagram on their website shows the yellow should connect to the coil.

mbell wrote:Going back to Vince's original questions. The Red and yellow wire aren't original so you need to do some testing. I'd guess your tacho has been converted to RVC, so I'd agree with Foxie on likely one being 12v supply to coil (possibly connect to a white wire behind dash) and one being coil negative connection for the tacho. So I'd start by testing for 12v on them switched by the ignition, then check to see if either is connected down to the coil.


I tested white (which, tracing back shows it to be is a continuation of the two original whites), and the white /black. Both showed 12.5 volts with ignition on.

Removing the (new) white lead from the coil cut voltage to the white/black. So I'm assuming this should go to the yellow. Red to straight white.

Note to self. Take image BEFORE removing wires!

Once the fuel pump is fixed, and the carbs fitted, I'll hopefully be able to give it a try.

Vince
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