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Old 12-20-2008, 03:33 PM   #1
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Default simple tach question

ok, you know how if you follow braineack's guide and get a diyautotune wiring harness, you end up with two spare IAC wires afterwards? How do I rig one of these wires to send my tach signal? Basically what I need to know is what those two wires are, according to megatune. I poked around and tried a couple different 'tacho output pin' settings and jabbed those wires with a voltmeter, but they display nothing at all.

Also, I have to build a tach driver circuit to get this to work (its a 97) and I already built the circuit, but:

that +12v ignition at the top, do i splice that into one of my coil pack ignition wires?
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Old 12-20-2008, 05:22 PM   #2
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The "Spare" and "IAC" pins on the DB37 have no direct relationship to anything in MegaTune. You just wire whatever internal function you need and wire that through whatever pin you have available. When you configure these "multipurpose" settings in Megatune, they will be referred to by their internal designation (ie: JS2) rather than a specific pin on the DB37.

You can pull the +12 from anywhere, including the 12v input to the MS directly on the board before the regulator.

So, for tachOut, you're first going to use MT to select which internal pin the tachout is on. We'll pretend you chose JS3. So, run a wire interbnally from JS3 to where it says "to the selected pin..." in that drawing. Now, the output (where it says "to tacho") needs to go to an unused pin on the DB37. You said you've got two spare IAC lines, so just pick one of those and wire the output of the circuit to it, then pick it up on the outside and run to the tach.
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