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MSD and factory tach??

Are you using the plug n play TFI harness or did you splice your MSD into the existing TC harness.

I have the plug n play TFI harness [from when I had the 5.0] and so I just used that, and the car ran great, everything was hooked up right Smile Smile but tach didnt work.

I am wondering if the plug and play harness has something to do with it?

Karnage how's your MSD hooked up?
I do Ported heads, intakes and rotated ported intakes, PM me for info.
84 Cougar XR7 Turbo
85.5 SVO 1E
86 SVO 1E

I used the plug and play harness and the car ran fine but the factory tach didint work. The adaptor is only about $25 dollars from summit so Ill order it rather than start cutting wires.
1985 2R SVO
1985 2A SVO
1994 Lightning

I just went through this with my Mallory install.

I do not think it has anything to do with using the adapter harness, the stock tack needs a voltage spike to start working. thats what the adapter provides.

BTW, on my TC, I was able to mount the tach adapter in a recess in the bottom of the battery tray, it out of sight and a little protected there.

Bob Myers
84 Capri RS Turbo
1/8th 6.29@110, 1/4 - 9.87@137

Guys, if you have an MSD, you DO NOT want anything hooked directly to the coil for signal purposes. The MSD outputs somewhere between 450 and 500 volts to drive the coil, and will blow the living shYt out of any tach that I know of. For comparison, the normal system drives the coil with 12 volts.

Probably the tach is most likely still connected to the wires that USED to drive the coil, but now trigger the MSD (red and white wires); that's where it's supposed to go.

It may just be my engineering paranoia, but it seriously scares me when you say that "... [it's] still connected to the coil".

Mine is hooked up with the plug-n-play MSD harness.I did read that autometer doesnt reccommend having they're tach hooked to the coil with the MSD.Mine has worked just fine for 2 years now.Not sure why.
84TC-gutted intakes-80mm maf-944 FMIC Greddy BOV 72lb inj
PPbig valve head-255LPH kirban-20psi-17"cntlines-65mmTB full 3" exhaust-on the way to 400hp

Because by using the MSD harness, the tach is not connected to the coil, it's connected to the input of the MSD. The output of the MSD connects to the coil (IIRC, the orange and black wires) and should be the only thing connected to the coil.

Happiness! Big Grin

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