View single post by edward_davis
 Posted: 08-11-2008 03:06 pm
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Joined: 07-06-2005
Location: Eugene, Oregon USA
Posts: 162
The factory tach gets its signal through the input wire for the coil.  The wire runs from the ignition to the tach and then onward to the coil.  The tachometer gets its reading by measuring the changes in current in the ignition wire: inside the unit is a little transformer, with the ignition wire wrapped around one side and another wire with many more windings on the other.  This is not at all how modern tachs work, so going to an aftermarket tach requires a bit of rewiring. 

When you pulled the speedo, did you get the whole gauge cluster out?  I pulled mine out with great difficulty the first time, but after sanding down and painting the "spike" that holds everything together, and adding a bit of grease when I reassembled it, I can now pull it out with two fingers and get easy access to the back of the gauges.  See my above post from 7-05.