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Old 02-20-2011, 06:14 PM
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HEI distributor with Autometer tach problem

Sorry if this has been posted before, I did a quick search and didn't find this posted. I have a '72 Chevelle 454SS. When I bought the car the factory tach wasn't working. I assumed it was just broken. I bought a new Autometer 3900. I wired this bad boy up and ...... nothing. Light works, but needle doesn't work. It is wired correctly. I have played with the connector, taken the cap off the top of the distributor and the yellow ground wire to the tach connector looks fine and intact. I assume it is grounded fine because the light works? I'm stumped, would a faulty coil cause something like this? Car runs great, just not tach. Any suggestions? Thanks in advance!

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Old 02-21-2011, 03:56 AM
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sounds like you got the wrong wire from the dizzy
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Old 02-21-2011, 07:16 AM
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I guess I should have said the yellow negative wire from the coil. It is the one that says tach on the cap. Really making me scratch my head. It is really simple. Should work, but doesn't?
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Old 02-21-2011, 08:00 AM
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This is a picture of the type of coil. Hooked green tach wire to end prong on yellow wire. Is that right? It says tach on it?
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Old 02-21-2011, 08:07 AM
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Yes that is correct. My 34 died yesterday after running down some electrical gremlins, no fire. Traced it down to the coil on my MSD distributor. The flimsy connection to that prong with the yellow wire was the culprit, it had broken right off. Pulled the coil and re-soldered it back on and good to go.

Vince
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Old 02-21-2011, 09:10 AM
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Yeah, I checked the wire. It seems intact. I am new to this stuff, so please bear with me here. Could I have the wrong coil in the distributor? Would that cause both tachs not to work (factory/autometer)? Do you think replacing the coil would solve the problem?
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Old 02-21-2011, 01:37 PM
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It sounds like you have it wired right, so maybe its time to buy a new coil. A stock Delco coil is fairly cheap to purchase, and it will work fine with your vehicle. You don't need to go for anything expensive in aftermarket ignition parts.

If that tach terminal is working, it should also show a reading when you attach a a tach-dwell meter. If you can borrow a meter from someone, you could verify that you are getting a tach signal on the terminal.

Bruce
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Old 02-21-2011, 03:55 PM
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Sounds like it's wired correctly
Is the green wire terminal at the coil making good contact? Id do a continuity check from the other spade connector on the yellow coil wire and the green tach wire just beyond the coil connector and again at the tach if no continuity .. Might try running a temp wire in from the window from the coil to the tach and eliminate the green wire......do you know anybody you could try a swap with..... that would eliminate the coil.
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Old 02-21-2011, 05:01 PM
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Changed out coil a minute ago and....nothing!
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Old 02-21-2011, 07:18 PM
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Try the continuity check from one end of the tach wire to the other end. There has got to be a short in there somewhere. Try running a jumper from the coil to the tech..... eliminating the green wire altogether
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Old 02-21-2011, 07:25 PM
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How do you have the Tach itself wired, as far as the rest of the wires on the tach?? What are the wires hooked to??
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Old 02-21-2011, 08:10 PM
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Red - Ing (fuse box) also ran off Acs (fuse box)
Black - Chassis ground
White - Headlight (fuse box)
Green - Tach terminal (though connector also ran clamped directly to prong on yellow wire)
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Old 02-21-2011, 08:18 PM
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Green wire coming in from right side saudered to brown wire attached to tach terminal



Sorry pic is so small
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Old 02-21-2011, 09:19 PM
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Just bought a tach filter online. That would be way too easy if it worked. Probably won't, how is that for pessimism!
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Old 02-22-2011, 03:51 AM
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green wire soldered to brown wire? your pic didn't come thru.
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