Speedo needle behaves like the tacho... but why?

[Troogly]

Hi

Had a great trip to the Growl yesterday - what a brilliant event. All fine there and back - except the last mile home. The speedo starts behaving like a tacho. With the car stationary, the speedo needle rose with engine speed just like the rev-counter. Even the mileometer starts clicking ahead in 1/10ths of a mile when the car is stationary and engine running. Looks like the speedo is picking up the signal to the tacho - but I don't know from where or why.

All OK otherwise. I did change the ignition amplifier about 3 days ago, and until now that was all fine (can't believe that would make any difference would it?) and did have to change the terminal fittings to the ign. amp.

I have a 92 Griff with LT77 gearbox. Speedo transducer changed last year (and all OK since then). I'll find out more today, but fault does appear to be intermittent.

Any insights on this sudden electrical problem much appreciated....

Thanks

[jesfirth]

I had that exact fault (also intermittent) on my 400se - it was a bad earth behind the dash

[davetherave1970]

I had similar.

Here