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Discussion Starter #1 (Edited)
Hi
I've searched and can't find the answer.This Sun Tach only has 3 wires,a Ground,a Trigger,and Ignition Switch???

This is going into my 74 Vega 383,I've installed a MSD Pro-Billet dizzy( ;)) and a Mallory VIa Electronic Ignition.I've got the trigger connected,the ground on,the light hooked up,but I don't know what to do with the Ignition switch wire.The motor is fresh and has never been fired,and I'd sure like a tach for break-in.

Should this Ignition Switch wire go to a switched 12 volt source?

Thanks-Hoonbash
 

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Doc here, :pimp:

Yup..Just find any Switched , Fused Source that goes on / off with the key..and it should be all good provided your MSD doesn't require a Tach adapter...

Doc :pimp:
 

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What year/style of Sun tach only operates off three wires?

I ask cause the Sun tachs I own all have four wires to them.
 

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Doc here, :pimp:

If you have a four wire it's because you have INTERNAL Illumination.

His , by the hole at 12 O'clock, is EXTERNAL Illumination..the socket provides a black and Red wire, or a Red and Finger tang for ground on the socket..

Doc :pimp:
 

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Doc here, :pimp:

Some of the OLD Tach units had calibration/Amp Card boxes as well as the remote mounted head..MANY of the OEM's went this way also (and were build specific..E.G., 4,6,or 8 Cylinder) and required the "Box" or board to be changed with the upgrade of say 6 to 8 Cylinder..(no little select switches..)

Shortly after , Everybody went to one~piece head units, as transistors got smaller, ran cooler, and linear Op amps came on the scene..It also became a simple thing to use a 4, 6, or 8 select switch by selecting inputs (or matrix them ) into a Chip input..

Some of the older OEM Tach units required a Buffer / Shaper between the coil and the sensor wire to shape and attenuate inputs..These looked like common coil filters, and a lot of guys mistakenly toss them during tune ups..The result is the tach either is grossly in error or flat dies within a few days..older Camero And Corvette are common for this. (I Have a Stock room shelf full of Corvette tach calibration boards that need rebuilding, if , I EVER get round to it.. )

What They really are is two Resistors in Parallel, and two mica bypass caps in series with each Parallel resistor, to make the wave form more "user friendly" to the Tach Electronics..Very few Of these systems are around nowadays...

Doc :pimp:
 

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Before the mid-1907s my experience with a tachometer was, well nothing.

I was given one of the hood mounted tachs like the early-70s GTOs got but since I had no idea what/where/who the wires went my one time attempt of hooking the tach up fried the insides.

I still own the tach. It ain't worked in 30 years.

:(
 
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