Had the same problem years ago and modified capacitor of tach as shown here
and solved problem.
http://www.healey6.com/Technical/Calibrate%20Tach%201.pdf
Jerry
> Tom -
>
> I'm with greg on this one. That little white wire has the most
> current and variation in current going through it than any other wire
> in the car. That creates a situation where that wire will increase
> resistance with so much use, and it sort of snowballs from there. I
> suspect that if you replace that wire, or at least replace the
> terminals with good soldered connections to the terminals, you will
> fix this problem.
>
> Alan
>
> On 8/19/11, Greg Mandas <gmandas at yahoo.com> wrote:
>>
>> Just a swag here, but my mechanic says my tach is running high because the
>> wire the tach reads is old and therefore has higher resistance (?EE's?) He
>> says he typically runs a new wire, therefore with lower resistance, o fix
>> the problem, barring a complete harness replacement.
>>
>> That being said, and the fact a warmer wire has higher resistance, sounds
>> like it should run higher at warmer temps.
>>
>> Sound Right?
>>
>> Greg
>> 65BJ8
>>
>>>
>>> On 8/18/11, Tom <ah3000me at gmail.com>
>>> wrote:
>>>> I've noticed that when I drive to work in the morning
>>> when it's cool
>>>> (50-60F), my tach shows about 2500 RPM at 65
>>> MPH. When I return home at
>>>> night when it's warm (80+ F), my tach shows about 3000
>>> RPM at 65 MPH.
>>>>
>>>> Any ideas about what's going on?
>>>>
>>>> thanks,
>>>>
>>>> Tom
>>>> _______________________________________________
>>
>>
>
> --
> Sent from my mobile device
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