Lotus Elan

Tachometer troubles

PostPost by: Rokkbert » Thu Mar 19, 2015 4:44 am

Hello all,
I have a 1969 federal lotus elan plus 2 and the tachometer isn't working. It's a smiths tach much like the one pictured. I've checked the original wiring diagram to make sure that the tach is wired correctly, which it appears to be (I say appears to be due to the tach being installed in the dashboard and a little bit difficult to see behind, however I got a scope inside, took some pictures and all the colours match to the diagram). The tach worked before a completely new wiring harness was installed so I know the gauge itself isn't faulty. As of now I'm thinking I've wired the volts stabilizer wrong or there's a problem with the actual stabilizer component. Either way it would be much appreciated if anyone could chime in with other possibilities.

Ps. The reason I haven't checked to see if the volts stabilizer is wired incorrectly is because it is currently almost 10:00 and rather cold outside, I will check in the morning
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'69 Lotus Elan Plus 2

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PostPost by: rgh0 » Thu Mar 19, 2015 6:14 am

The tach should not have a power supply from the voltage stabiliser, although the voltage stabiliser may be mounted on the back of the tach and share an earth connection and the 12 V connection to the stabilser may also feed the tach

The tach has

1. A 12 volt supply
2. The white wire to the ignition coil that runs though the tach via a couple of bullet connections. It has no electrical connection connection to the tach there is just a coil for current sensing inside the tach
3. A black earth wire

4. Instrument light bulb connections

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PostPost by: Rokkbert » Thu Mar 19, 2015 6:32 am

So what do you think the problem is? Keeping in mind that all wires coming from the tachometer are correct, and the gauge works.
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PostPost by: rgh0 » Thu Mar 19, 2015 6:42 am

You talk about the voltage stabiliser in your first post - this should not be connected to supply the intermittent 10V power it produces to the tach. If it is then that is the problem.

If the wiring is correct and that is a big "if" as most people dont understand how current sensing tachs work and often wire them wrong and the tach still does not work then it will be a failed internal electronic component, most likely one of the capacitors.

You say the tach does not work - do you mean it does not move at all or are there other symptoms

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PostPost by: Rokkbert » Thu Mar 19, 2015 6:52 am

By " the tach does not work" I mean that the needle does not move at all, it is not an intermittent problem. Furthermore, the tachometer did work before a new wiring harness was installed. And when I say the wiring is correct I mean that compared to the wiring diagram in the owners manual, all of the wires match those currently connected to the back of the gauge. The only reason I mentioned the voltage stabilizer is that it seemed to be the next thing to check after the gauge itself.

I would like to add that I am not a "wiring guy" and that I am simply following what I can see in the diagram.
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PostPost by: john.p.clegg » Thu Mar 19, 2015 7:24 am

I'd go for that little loop of white wire wrapped around the sensing post...bet it's not connected..are there bullet connectors on the ends...

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PostPost by: Rokkbert » Thu Mar 19, 2015 7:30 am

Thank you :), I'll have to try that tomorrow. It's amazing how difficult it is to see when you've got all that other dash wiring blocking your view!
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PostPost by: rgh0 » Thu Mar 19, 2015 10:14 am

john.p.clegg wrote:I'd go for that little loop of white wire wrapped around the sensing post...bet it's not connected..are there bullet connectors on the ends...

John :wink:


Hi John
I think a 69 tach should have the induction loop sensor internally and the white supply from ignition to coil should go through a couple of bullet connectors on the back.

A federal 69 car may also have a ballast ignition setup and depending on how this has been wired maybe the normal running power supply to the igntion is not live?

It all get back to how well the new loom was installed I guess

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PostPost by: billwill » Thu Mar 19, 2015 12:49 pm

Bullet style with internal loop
Image

Earlier style with external loop

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The photos are from the existing photo gallery on this website.
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PostPost by: Grizzly » Thu Mar 19, 2015 1:35 pm

I assume you haven't got an Electronic ignition?

I think if it was me assuming the car runs and the white wire goes through the tacho and hasn't been bypassed, the Power is 10v or more going into the feed and the negative is good i'd be tempted to fit a Spiyda kit https://www.spiyda.com/magento/index.ph ... board.html
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PostPost by: Rokkbert » Thu Mar 19, 2015 3:40 pm

I'll have to do some more trouble shooting today, tracing wires back and checking connections, that sort of thing. no I do not have electronic ignition, it still has the original points. Also my tachometer is the first image shown with the internal loop. I've been trying to do this with just the dash pad out but now I'm thinking I'm just going to remove the steering column and take the whole dashboard out
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PostPost by: Grizzly » Thu Mar 19, 2015 3:49 pm

Probably not a bad idea to drop the steering column, When i was having issues i took the column out and it gives you quite good access to the back of the tacho.
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PostPost by: Rokkbert » Thu Mar 19, 2015 3:57 pm

Yeah, I suppose in the end it's just down to getting out there and chasing down wires. I was just curious if maybe there was a common "weak link" in the system, or that sort of reoccurring problem.

Thank you for all of your help on this matter

Robert
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'77 Lotus Esprit
'86 Lotus Esprit HCPi Turbo
'68 Lotus Europa S1-B
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PostPost by: Grizzly » Thu Mar 19, 2015 4:16 pm

Rokkbert wrote:Yeah, I suppose in the end it's just down to getting out there and chasing down wires. I was just curious if maybe there was a common "weak link" in the system, or that sort of reoccurring problem.

Thank you for all of your help on this matter

Robert

In my case yes 40+ year old electronics :( with one of my Loti my tacho was all over the show then one day just died so i just replaced the Circuit board and ran it -VE so it works solidly now.

The thing is if you have seen the Tacho Work and the engine starts and runs my moneys on an Internal fault but by all means check there is at least 10v on the Feed (It reduces its own power to 10v internaly anyway so it will work with an external Stabilizer) then a Good ground to the Body of the gauge.
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PostPost by: john.p.clegg » Thu Mar 19, 2015 4:40 pm

I don't like using the stabilised 10v as it's made up of pulses ?

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