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Strange one yesterday, when indicating left the tacho was going nuts, going from zero to high at the beat of the indicators. Engine speed was normal, as was the right turn indicator.

Initial thoughts were a blown indicator bulb but when I got home I had a look and front, rear and side lamps lit up as expected. This morning I took the bulbs out and had a closer look. The front one had rusty corrosion in the lampholder and the bullet connector was a bit green. I tidied it all up with contact cleaner and clean cloths and success, no more dancing tacho.

I have no idea why it would have affected the tacho.

Hi poprivet,
Something was going on there no doubt.
I don't think I will ever fully understand the electrics in the auto world.
Glad you solved the problem though.
Take care and stay safe.
Andy

Interesting one!
I guess the only common connection would be the earth and the corrosion you cleaned up meant that the normal path to earth for the indicator lights was higher resistance than the path via the tacho and hence your dancing needle. Just a theory