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Smith's tach question

To: british-cars@autox.team.net, Spitfires@autox.team.net,
Subject: Smith's tach question
From: "John T. Blair" <jblair1948@cox.net>
Date: Fri, 22 Sep 2006 16:26:14 -0400
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.  I know I've had one like that on one
of my cars, but for the live of me I can't find anthing about it.  I thought
I had one like that on my Morgan, so I crawled under the dash a couple 
of nights ago.  Nope, mine has got 3 terminals.

The problem is he didn't flag the wires and can't figure out how to hook it 
back up.  We know one side connects to the negative terminal on the coil.  
The problem is where does the other end connect.

Logic says it must go to 12V. OK, BUT, what happens if the points are 
closed and the ignition switch turned on?  Instant short.  So there
must be either a resistor (like a ballast resistor) or a resistive piece
of wire.  

If anyone has one of these magnetic tachs on something, how is it wired?

TIA

John


John T. Blair  WA4OHZ     email:  jblair1948@cox.net
Va. Beach, Va             (eBay id: zebra48-1)
Phone:  (757) 495-8229

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