Lotus Elan and Lotus Elan Plus 2 Forums

Oh Joy

It's time to break out my electrical test tools. My tame mechanic could get my Plus 2's horn working but he did do all the niggly little jobs that I didn't want to do like changing the roll bar bushes, changing gearbox and diff oil etc so that job no 1 - and I suspect its earth hunting, but I've ordered a new two tone air horn anyway. The second is that the Tacho flicks around when I turn the ignition off - now I'd assume this another earth issue but is there anything else that causes it?

It needs some power source to register, presumably from the ignition circuit. Does it work normally otherwise?

Sneak current?

Thanks Tkskip - yes it does seem to work normally andits only just started to act up! I've been messing with earths behind the dash, and have a couple of other issues - such as the horn not working, so its back behind the dash with a probe and meters this weekend, and I'm also replacing the ign switch and solenoid to hopefully sort out an intermittant starting issues - i.e turn the key to start and nothing, waggle it maybe get a click, waggle again and everything works normally - well normally for a Lotus!

The tacho works by measure current pulse to the coil which it can "convert" to RPM (two pulses a cycle). So it could be detecting pulses or back noise from the coil (guess). So I check the behavior with the coil disconnected. I'd start by unplugging the coil and testing. If it still does that I remove the coil supply and wire from rear of the tacho and re-test.

If it still does it you know the problem is in ground or 12v supply. I'd probably create a temp gnd connect to tacho as next step.