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engine wouldn't start
#1
So yesterday I went to start my mustang and it would fire for like a second then die. Today same thing, the only thing I did since the last time it ran was remove the gauge cluster. Come to find out (I think) the tach grounds the ign coil. Hooked the tach back up and it started and ran like a dream.

Is this how it's supposed to work or did I wire the coil wrong?

Thanks for looking.

Jayson
[Image: 36319488731_8f2a376549_z.jpg]
73 Mach 1 Mustang
89 Dodge Shadow ES
94 Jeep Wrangler

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#2
Take a look at this

http://www.mre-books.com/shopmanuals/dow...o10023.pdf

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#3
Thanks but there's only two pages of wire diagrams. I'll check my factory shop manual.

Jayson
[Image: 36319488731_8f2a376549_z.jpg]
73 Mach 1 Mustang
89 Dodge Shadow ES
94 Jeep Wrangler

  Reply
#4
Not sure if it was the tach, but you might try unhooking the Tach again to see if the engine will start! Could have been a fluke.
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#5
The factory tach is wired as part of the ignition circuit - in a nutshell: 12V+ from ignition switch through tachometer, through resistor wire to ignition (+) side of coil. If the tach fails or is unplugged there is no power to the coil so the car will not run. It will fire when the key is in start because the bypass wire from the solenoid is supplying 12V to the coil during start.

Bob

Tachs, Voltmeters, Headlight kits, Wiper delays and more at
[Image: smlogo.jpg]
Rocketman's Classic Cougar (and Mustang) Innovations, LLC
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#6
Good info, so not a fluke! U Da Man!
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#7
Yup need a tach or bypass the tach by jumping the plug to the tach with a paperclip.
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#8
OLE PONY;30986 Wrote:Not sure if it was the tach, but you might try unhooking the Tach again to see if the engine will start! Could have been a fluke.

When I had the tach hooked up it ran fine, I unplugged the tach and the motor shut off.

After looking at the wiring diagram I found out that there is supposed to be another wire spliced before the tach that goes to the coil and gives it a constant 12v when the igniton switch is in the on position. I just got in from testing my theory and it works great with a jumper and I found the wire so I just need to extend it to make it work.

Thanks for the info guys.

I highlighted the wire that's not connected with blue

[Image: wire-1.jpg]

Jayson
[Image: 36319488731_8f2a376549_z.jpg]
73 Mach 1 Mustang
89 Dodge Shadow ES
94 Jeep Wrangler

  Reply
#9
Jayson,
By using that wire you are bypassing the resistor wire and delivering a full 12V to the coil and (if you have them) points. This will shorten the life of both significantly.

As 72HCODE mentioned - if your tach is bad, unplug it and add a jumper to complete the circuit across the tach wire plug. This will keep the ignition circuit working as designed.

Bob

Tachs, Voltmeters, Headlight kits, Wiper delays and more at
[Image: smlogo.jpg]
Rocketman's Classic Cougar (and Mustang) Innovations, LLC
  Reply
#10
TheRktmn;31040 Wrote:Jayson,
By using that wire you are bypassing the resistor wire and delivering a full 12V to the coil and (if you have them) points. This will shorten the life of both significantly.

As 72HCODE mentioned - if your tach is bad, unplug it and add a jumper to complete the circuit across the tach wire plug. This will keep the ignition circuit working as designed.

I see your concern but why does the factory wire diagram show a switched 12v wire going from the starter relay/solenoid to the coil.

Jayson
[Image: 36319488731_8f2a376549_z.jpg]
73 Mach 1 Mustang
89 Dodge Shadow ES
94 Jeep Wrangler

  Reply
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