Lotus Elan

Elan Plus 2 S130 panel light rev counter electrical issue

PostPost by: davieroy » Fri Jul 19, 2019 4:53 pm

This is driving me mad. When I turn on the panel light switch my rev counter stops working. I turn the panel lights off and the rev counter bursts into life. I have looked at the wiring diagram but I can’t understand what is happening. Anyone got any ideas? Regards, Roy
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PostPost by: billwill » Fri Jul 19, 2019 5:24 pm

Clearly there is insufficient voltage at the power feed to the rev counter when the lights are on. That will be either a dirty joint somewhere (maybe a dirty earth) or perhaps the power for the lights and the rev counter has been taken after the voltage regulator (for the thermally operated gauges).

In fact both the rev counter and the panel lights do not need regulated power. The rev counter has its own zener diode inside and the panel lights are just simple bulbs.
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PostPost by: mbell » Fri Jul 19, 2019 5:48 pm

I'd put my money on the taco ground connection. The tacho light grounds through the tacho body and tacho Earth connection. Increasing the current flow that could increase the voltage across a poor connection, which might drop the voltage across the tacho below the diode threshold.

The tacho Earth connection on mine is just a loop connector on one of the tacho mounts so pretty easy for it not to be very effective.
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PostPost by: davieroy » Fri Jul 19, 2019 6:07 pm

The tacho light doesn’t come on either (neither does the speedo light either) but all the other instrument light bulbs are working. Could this point to the earthing?
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PostPost by: EPA » Fri Jul 19, 2019 7:46 pm

The tachometer could actually be earthing through the instrument bulbs until you switch the panel lights on. As said previously the earths are looped between the mounting studs of the various gauges.If one of these loops is missing or has a bad connection it could produce your symptoms. I would run an earth to the tachometer case to see if it resolves the issue.
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PostPost by: davieroy » Fri Jul 19, 2019 8:04 pm

Thanks all. I’ll have a go and come back to you with an update.
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PostPost by: davieroy » Fri Jul 19, 2019 8:36 pm

Gents. In the fading light here in rural North Yorkshire, I touched the tacho case with a long screwdriver and ran a wire from that to a good earth - the tacho came to life as did the instrument bulb! That’s the problem, no earth from the tacho so thank you all again.

Next issue is how do I get to the back of the tacho to connect a new earth wire to it, does the dash have to come out ? (please say no).

Regards
Roy
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PostPost by: mbell » Fri Jul 19, 2019 9:21 pm

Good news.

You should just be able to remove the under trim from the dash and reach up. I've been able to remove/refit that way.The earth connect should be on one of the mount studs and might be hanging somewhere in there not connected. If you can find it, its just a fiddly job to remove the thumb nut, slide the ground wire over and re fit the thumb nut.

If you can't find it just make a new earth wire and mount it to the stud the same way.
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PostPost by: davieroy » Fri Jul 19, 2019 9:39 pm

Just a thought, is it possible to get to the back of the tacho via the air vent on top of the dash? You may have gathered, I am relatively new to Elans.
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PostPost by: prezoom » Sat Jul 20, 2019 2:39 am

On my S2, the ground for the tach and the speedometer are on the same wire, same for my Plus2. As stated, the ground connection is under the thumb nuts holding the instruments onto the dash. One connection to each instrument. I find it easier to work on those instruments by removing the steering wheel. Not entirely necessary, but just easier.
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PostPost by: types26/36 » Sat Jul 20, 2019 6:36 am

You can remove the speedometer which is not difficult then work through the hole to access the tachometer........just realised its a plus 2 so maybe It’s not as easy as the two seater.
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PostPost by: davieroy » Sat Jul 20, 2019 3:28 pm

Finally sorted it. Removed the speedo as advised, first removing the fresh air vent next to it and found the tacho earth wire was not connected to anything. I soldered a new bullet connector to it and connected to an earth. The instrument light now connects to the same earth and everything works. Thanks again for all your help - Roy
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