At 04:26 PM 9/22/2006 -0400, John T. Blair wrote:
>I'm trying to help a fellow who is restoring a 1974 British Ford Escort.
>
>He's got a problem with the tach. It's Smith's with a magnetic
>pickup, a wire loops around a pickup piece. .... how is it wired?
Same as 65-66 MGB. Run a white wire from ignition switch through the
loop an on to the coil. With ignition on and points closed the coil
has 3 ohms resistance which limits the current to 4 amps. Points
opening when engine runs interrupts the current. Tach counts the
induction pulses.
If you need to convert it to negative earth, see here:
http://mgaguru.com/mgtech/electric/et202a.htm
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