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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Factory Tach Question.

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Old May 8, 2014 | 04:33 AM
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RadioControlGuy85's Avatar
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Factory Tach Question.

hey guys,

i have a question about the factory tach.

we bought a cluster about a year ago with the factory tach.we installed it and it worked fine.but now we put a new coil in the truck,now the tach will not work.it will jump when you first turn the key on,then it dose nothing.

but the neg side of the coil has current on it is that right??

the new coil is a Ford TFI Coil, Street Fire
 
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Old May 8, 2014 | 05:15 AM
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yes. the tach feeds off the negative side of the coil

I have the wiring diagram but there is no easy way to insert a picture here.
 
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Old May 8, 2014 | 09:07 AM
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You can always wire it up independently. It has the same inputs as any aftermarket tach, with the addition of an extra ground terminal so it can be used with both 6 and 8 cylinder engines.
 
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Old May 8, 2014 | 11:48 AM
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What year truck? Engine type?
What type of ignition module are you using?

Just plug the old coil back in for a quick test, just the wires no need to bolt it in, to see if the Tach is good.

Why did you have to buy a new coil? Did something break?

Jim
 
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Old May 8, 2014 | 02:09 PM
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Good suggestions and questions, Jim!
 
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Old May 8, 2014 | 03:21 PM
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its a 85 f150 with a 4.9 300 inline6

we replace the coil,cap,plug wires.

it was working before we parked it.now after we got the engine back together it just jumps.

also, the neg side of the coil is hot. is that right?
 
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Old May 8, 2014 | 03:33 PM
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Originally Posted by RadioControlGuy85
its a 85 f150 with a 4.9 300 inline6

we replace the coil,cap,plug wires.

it was working before we parked it.now after we got the engine back together it just jumps.

also, the neg side of the coil is hot. is that right?
At Idle or key ON not running?
The answer to the amount of voltage present at the NEG side of the coil depends on the type of IGN module you have and where it is running.
Are you using the stock one that is mounted on the Dist?
 
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Old May 8, 2014 | 03:36 PM
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Get in thar between the negative coil terminal and ground, let me know what you think...
 
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Old May 8, 2014 | 03:51 PM
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Originally Posted by JimsRebel
At Idle or key ON not running?
The answer to the amount of voltage present at the NEG side of the coil depends on the type of IGN module you have and where it is running.
Are you using the stock one that is mounted on the Dist?
yes when key is on and acc the neg side of the coil is hot.yes its the one that sets on the side of the dist.


Originally Posted by Tedster9
Get in thar between the negative coil terminal and ground, let me know what you think...
what do you mean???
 
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Old May 8, 2014 | 04:37 PM
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If you are using a test light, the light will glow the same on both side of the coil with the key ON and engine not running. Same voltage on both sides of the coil.

When the engine is running the NEG side of the coil will have less voltage, or a dimmer test light.
 
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Old May 9, 2014 | 03:56 PM
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thanks for all the help.

we got it fixed.
one of the wires was hooked up wrong on the dist connector.
 
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