Lotus Elan and Lotus Elan Plus 2 Forums

My rev counter intermittently (about 1:10) gets a full deflection momentarily when I switch the ignition on. It is not a problem, but I was concerned about impending failure or a feature of more serious electrical failure.
It also from time to time over reads (typically 500 rpm at 60mph in 4th gear). I read previously on here this may be due to ageing electronic components. Are these two problems linked?
1966 S3 Coupe, previously (previous owner) converted to alternator and negative earth.

Rediscussed recently, in fact still ongoing:

lotus-electrical-f38/rev-counter-damage-from-reverse-polarity-t42507.html

Thanks, Bill. The thread and links make for interesting reading and although I got a grade A at physics A level, it was 43 years ago, electronics knowledge untouched since (not much call for it doctoring)
I think I?ll get it looked at by someone who knows what they?re doing.

Malcolm

Be sure to read all of this topic too.

It was just added to the other topic I directed you to.

lotus-electrical-f38/tacho-repair-t41110.html

I have a different problem with the rev counter on my 1969 S4. Just got the dashboard back together, fired up the engine, no rpm on counter. I then noticed if I rev the engine, the pointer does move a little bit. Really racing the engine brings the reading around 1000 rpm. So it is showing 20% of reality.

What did I do wrong? It did work correctly before I took things apart.

I'm no electrician but my guess would be that the instrument is not powered .. possibly bad or missing connections on the feed or earth. The earth is via a "daisy chain" of small ring terminals that connect the instruments together, fitted under the thumb nuts of the clamps...easily overlooked. There may also be a an earth spade connector on the tacho case itself (can't remember for sure). If the main beam warning lamp and the panel lamp in the tachometer are not working either that would indicate a missing earth connection, if they do work then it's the power supply at fault.