WEIRD tach problem!!! Someone explain
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Senior User
Joined: Oct 2004
Posts: 481
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From: Tualatin, OR
WEIRD tach problem!!! Someone explain
My old Suntach II finally died and I decided to replace it with another one. I wanted to check the new tach before I installed it. Hooked up positive and negative to battery and coil line to negative post on coil. It didn't work. Just for the hell of it I put the coil wire on the POSITIVE post of the coil and it worked perfectly! My truck does have an MSD ignition which may be the reason for the opposite hook up. Can anyone explain what is happening? Will it hurt the tach to run it this way?
Elder User
Joined: Nov 2004
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You cannot hook the tach to the coil if you are running an MSD. This is probably why the old tach failed.
There is a tach connector on the MSD box. Hook it there. Read the tech notes on the MSD web site if it does not work. I believe some tachs may require a tach adapter from MSD if it does not work when connected to the tach terminal.
There is a tach connector on the MSD box. Hook it there. Read the tech notes on the MSD web site if it does not work. I believe some tachs may require a tach adapter from MSD if it does not work when connected to the tach terminal.
Senior User
Joined: Feb 2011
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From: Albany, Georgia
i got a pretty heafty MSD starter, coil, wires, etc on my trans-am. i have one of those performance tachometers with the light up light that activates at the best shift time (for economy) and the starter required a hook up for it. so it may be an MSD thing that requires them to have therir own hook up? haha
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Senior User
Joined: Oct 2004
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From: Tualatin, OR
The old tach /green wire was connected to a green/yellow stripe wire under the dash before the MSD. It worked that way for years. Weird! It sure works well now the way it is hooked up. I won't run it though and try to find the msd wire to connect it to. Thanks.
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Senior User
Joined: Oct 2004
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From: Tualatin, OR
f100jim... thanks! I just went out to the truck and wired in the green tach wire to the tach output terminal on the MSD box. Worked like a champ!!! Thanks again. It sounds like I don't have a clue but when I bought the truck 20 years ago, the original aftermarket tach was already installed along with the MSD. I started over with the new tach and didn't use their old connection set up. I'm not sure why they didn't wire it up like it is now??? Like I said, they had it piggy backed into a green wire into the under dash harness for the coil line. After thinking about it all day.... maybe the previous owner installed the tach before the MSD ignition. That would explain things.
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