Throttle pot and the speedo/rev counter.

[TV8]

For some time, my speedo has been been dropping back when I fully lift off the throttle and the rev counter has a mind of its own for even longer. Hard acceleration steadied everything up and I assumed that this was down to the load on the diff for the speedo but didnt have a clue about why the rev counter counted properly.

The first proper drive for while today and the speedo was absent most of the time and the rev counter all over the place as normal. Crusing along playing guess how fast I am going, I noticed that there was a direct link between touching the throtle and the random movements in the two big dials.

So my question is, can the throttle pot affect the speedo and rev counter in this way?

The car is an early (L reg) 400 and generally runs well. A bit fluffy on cold start and occasionally a bit shunty but other wise good.

Thanks in advance

Graham

[blitzracing]

The simple answer is no, there is no signal of any type between those two. Id suspect a earth point some where for the as instruments, or dancing tacho's can be caused by Magnecor leads / bad earths.

[spend]

Dash earth normally flickers the other dials as well, not as much maybe as the speedo & tacho but generally evident. If you have the black earth connected to the alt that can do funny things, I think some had it connected to the otter switch others to the head grounds ~ none of which ever made much sense to me... as it's intended to output a tacho signal on most alts for diesel LR's AIUI?

[TV8]

Thanks for responding. Is the dash earth the one that is connected to the transmission tunnel?

Also, is there anything else linked to the trottle that could cause the two dials to be affected?