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rackolamb1

240z tach and Jacobs Electronics help needed

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Hey guys, I've got a Jacobs Electronics Mileage Master from an older project of mine that I've recently installed into my 71 240z. The engine is an 83 L28ET with stock ECU. Everything runs great, but I'm not sure how to wire this setup up to my tach. I've searched and searched and can only find info related to the MSD 6 boxes which have a tach output. My Jacobs unit does not have a tach output, so I'm stumped as to how to hook up my tach. I do have the MSD 8920 tach adapter, but I am unsure where to tie it in.

 

Can I just use the (-) side on the coil and run that through the white wire on the adapter and then connect the red wire from the adapter to the tach? Any help on this would be greatly appreciated.

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Hey guys, I've got a Jacobs Electronics Mileage Master from an older project of mine that I've recently installed into my 71 240z. The engine is an 83 L28ET with stock ECU. Everything runs great, but I'm not sure how to wire this setup up to my tach. I've searched and searched and can only find info related to the MSD 6 boxes which have a tach output. My Jacobs unit does not have a tach output, so I'm stumped as to how to hook up my tach. I do have the MSD 8920 tach adapter, but I am unsure where to tie it in.

 

Can I just use the (-) side on the coil and run that through the white wire on the adapter and then connect the red wire from the adapter to the tach? Any help on this would be greatly appreciated.

 

The original tach on a '71 is current controlled, e.g. it is triggered by the current pulse going through the primary coil wire in the original setup. The Jacobs Milemaster works differently as it is a capacitive ignition, sending high voltage (400-600V) pulses to the primary coil wiring.

 

According to the manual (is this the right one? http://www.accel-ignition.com/pdf/341000_372446.pdf) the brown wire delivers a square wave signal to trigger an electronic tacho. You could convert your tacho to accept electronic signals (http://www.dinoplex.org/tachoconversion/), connect your MSD 8920 tach adapter to the brown wire of the Jacobs ignition (see MSD Manual second wiring sheet for current controlled tachos), or exchange your original tacho against a newer one such as made by Autometer and others.

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