Erratic tacho behaviour
Discussion
One for any electrical gurus: My tacho seems to go mad over about 3K rpm - jumps to 4 or 5 then back to 2. At idle its very slightly jittery. None of this behaviour reflects what the engine is doing, which is running fine. It all started the day after the charging warning light came on. The light stayed on, but the battery was definitely being charged, as it had 15 or so starts while the light was on over the course of 2 or 3 days. This was cured with a new alternator - I did think that the voltmeter in the car was reading very slightly higher than normal, but still under 14 volts (don't actually know how accurate these are). Aside from a new alternator, I fitted a new Bosch coil, plus a brand new ignition amp module. No change in the tacho behaviour. Cleaned the connections between amp and coil, checked the cabling to the tacho as far as I could. Nothing obviously amiss. Is it possible that the fault in the alternator may have damaged the tacho? Any other suggestions please? Stewart Warner gauge. 
Coil and ignition amp wiring polarity correct? Reversing the coil can have some odd effects although the sparks still fire (just in reverse flow 
).
Also, did it really need a new alternator? It's usually just worn brushes, a replacement brush set (actually the whole brush box inc. regulator) was about £12 and half an hour to change last time I did mine.
).Also, did it really need a new alternator? It's usually just worn brushes, a replacement brush set (actually the whole brush box inc. regulator) was about £12 and half an hour to change last time I did mine.
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