Crazy tacho!!

[fbenach]

Hello everyone, long time no see!!

So my R65 has been beautifully working for the last few year (I kinda re-did the whole bike using a lot of the help from the gurus here).

A few days ago I noticed my tacho needle jumpls like crazy from time to time, every time it behaves weird the little red light lits as well.
Then, notices it does it even works if I turn the indicators on!!!

Finally it started doing the following: it turns the headlight off if I put on a gear, so my headlight only wotks when I am in neutral!!

Naturally I started looking for shorts but all my harness and wires seem to be good!!!

What am I missing? Any suggestions?

Cheers and thanks in advance guys!!

[dogshome]

Hiya, I would say you have a bad earth. Either the one on the battery, the little spider under the tank or maybe on the diode board. Easy one first - battery to gearbox. Little one under tank next.

Also check your voltage when running at the battery in case your regulator is doing something it shouldn't.

[Justin B.]

I had similar issues on a 1980 and putting a ground strap between the forks and frame fixed it.

[Barry]

Another good reason for Justin's ground strap.   

I think this came originally from the Motobins website

Steering Head Races on R45/65, R80ST models can often suffer premature failures, their outer races showing regular dark lines where their rollers have made contact. These lines are the sign of electrical erosion, probably due to tracking across the tachometer's ignition coil connection on the printed circuit board to the steel case of the instrument. Make sure that you earth the upper fork yoke to the main frame earth below the fuel tank, to provide an alternative path. 

[Bob_Roller]

What year bike do you have ??
The early R65's had the main grounding or earthing point for most of the bikes electrical systems on the front ignition coil mount bracket .
It has been known to crack and cause odd electrical issues .

[fbenach]

Thank you gents!
I will surely use your advice and try to get down to the reason !!

My R65 is a 1979 model, dual disc!!