Tach Grounded = No spark!
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Tach Grounded = No spark!
Just had Betty's (Betty is my '82 F-100 w/ a single barrel on the 6-300... and I love her) engine rebuilt and stabbed in. I had hooked up an autometer 6k rpm tach and had no spark coming from the coil. So i did a little research and removed the ground on the tach.
Long story short: coil/dizzy work, tach don't.
I fully understand why the tach wouldn't work w/o a ground, and vaguely understand why the coil won't work with any kind of ground on it, but why can't I have the best of both worlds?!?!?!
Anyone have a clue as to how I can get this tach working without disabling the coil/dizzy?
Long story short: coil/dizzy work, tach don't.
I fully understand why the tach wouldn't work w/o a ground, and vaguely understand why the coil won't work with any kind of ground on it, but why can't I have the best of both worlds?!?!?!
Anyone have a clue as to how I can get this tach working without disabling the coil/dizzy?
FTE Legend
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From: Northeast, OK
You don't have it wired correctly would be my guess. The tach should probably have one wire to the Tach terminal on the coil, one to +12, one to ground, and one for lighting. But I don't know which color wires should go where. Do you have a wiring diagram?
Logistics Pro
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From: Martinsburg, WV
"Most" aftermarket tachs it is the green wire that is the rpm sense. Orange or white for lights. and Red for +12, black for chassis ground. The tach sense should go to the dark green with a yellow stripe at the coil, but I could be off by a few years. Regardless of color, the sense wire goes to the negative(-) side of the coil.
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I feel confident in the "correctness" of the wiring. Black to ground, green to neg terminal on coil, red to ignition-hot, and white to lights.
When it's all together the tach zeros out when the ignition lock is turned enough to provide a current, when I turn the lights on, the tach light comes on with the dash lights, but the coil just will not throw that damned spark. So I'm still looking for other answers.
Regardless, I will recheck all the wiring.
Thanks for the replies. I'll let you know how the next go turns out.
When it's all together the tach zeros out when the ignition lock is turned enough to provide a current, when I turn the lights on, the tach light comes on with the dash lights, but the coil just will not throw that damned spark. So I'm still looking for other answers.
Regardless, I will recheck all the wiring.
Thanks for the replies. I'll let you know how the next go turns out.
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on some cars, i've done a spark signal test using a test light over the wires to the coil, and on engines whose ignition coil is worn out and about to die, that simple test will prevent the coil from throwing a spark. so i'm wondering if your coil is oil and weak and a fresh one will run with the tach connected
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From: Exmore, VA
That seems to be one that I can't get the installation information on. Most of their tachs seem to use Green to coil - , Red for 12v, Black to ground and White for dash lighting feed.
Have you contacted the seller, if it's the link you sent, he is an authorised Autometer dealer. Autometer's sight is less than useless if your truck is older than 1991.
You have the DS-II system, coil - is dark green with a yellow stripe, coil + is red with light green. The Ford factory tach hookup is usually a pigtail on the coil - or in the dash harness to the cluster.
Have you contacted the seller, if it's the link you sent, he is an authorised Autometer dealer. Autometer's sight is less than useless if your truck is older than 1991.
You have the DS-II system, coil - is dark green with a yellow stripe, coil + is red with light green. The Ford factory tach hookup is usually a pigtail on the coil - or in the dash harness to the cluster.
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It is new, didn't have the battery in during installation until everything was in place, and it "zeros out (meaning that without the key turned the tach rests at about 300 rpm and goes to zero when the key is turned). So, I hope it isn't blown! Still not ruling anything out though. Is there a way to test it where it is?
I haven't touched the thing since yesterday but will be back on it in a few hours to check for proper wiring, good connections, proper settings, etc. etc.
Keeping on it... thanks for all the input everyone!
I haven't touched the thing since yesterday but will be back on it in a few hours to check for proper wiring, good connections, proper settings, etc. etc.
Keeping on it... thanks for all the input everyone!
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Do you have another vehicle to try it on? If not, you might be able to test it with a DVM by placing the meter between ground and the sensing wire and put the meter in volt mode. If you don't see +12v on the lead then turn the meter to resistance, but if you do see +12v then don't go to resistance as you might blow the meter. In resistance do you see low resistance, like below 100 ohms? If so, that could interfere with the ignition.
If you see voltage on the sensing lead then put a test light on it. If the light comes on then your tach is sourcing current and that could interfere with the ignition.
If you see voltage on the sensing lead then put a test light on it. If the light comes on then your tach is sourcing current and that could interfere with the ignition.
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There is another way to sort of test the tach. Take the input wire to the tach off the coil, and brush it against a good ground. All the tach does is measure the on-off of the ignition system, so by brushing the wire against ground, you are simulating the on-off of the ignition system. You should see the needle on the tach jump around slightly. If you are good and really get a intermittent connection to ground on the wire, you will get the needle to jump up several 100 rpm.
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Regrounded the tach and hooked up the green tach lead to the green yellow wire from the wiring harness that connects to the duraspark (rather than to just the neg coil terminal.
No luck.
Unplugged it.
Fired right up.
Plugged it in.
Works great.
Starts up smooth as can be!
Could I have "switched" something on in the tach?
No matter, I'm a happy camper and the truck is running beautifully. Thanks!
No luck.
Unplugged it.
Fired right up.
Plugged it in.
Works great.
Starts up smooth as can be!
Could I have "switched" something on in the tach?
No matter, I'm a happy camper and the truck is running beautifully. Thanks!