View single post by NigelK
 Posted: 12-11-2016 02:44 pm
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Joined: 07-16-2014
Posts: 171
An update. I had the tacho out again yesterday. Cleaned all the contacts with emery paper, replaced the female spade connector on the earth wire (as it had opened up too much to fit securely onto the male spade connector on the tacho casing) and checked that the earth was good. Then recalibrated the tacho again, this time ensuring the reading matched that on my multimeter when the tacho was in situ in the dashboard. All good, until I re-installed the tacho and it was reading low again. I started the car up again 24 hours later and the tacho was reading even lower. I am beginning to suspect that 41-year old electronics components are at fault here and that a full tacho refurb is required.

A fellow JOC member has suggested noise in the ignition circuit could be the problem. Worth noting that the tacho needle bounces to around 7,000 rpm when I start cranking the engine but settles down as soon as the engine fires. Is this normal? Or a sign of something amiss in the ignition circuit? Please note that I do not have the standard J-H ignition circuit in my GT - I have the Lucas Constant Energy system fitted i.e. 45DM4 optical trigger distributor and AB14 ignition amplifier.

Does anyone have any other ideas?