OEM tachometer wiring?
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Joined: Sep 2004
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OEM tachometer wiring?
I have a 92 F150 5.8L.
I have the OEM tach in the instrument cluster, however when I turn the key to the on position, the tach goes to 500 RPM. When I start the truck, it goes to around 2000RPM and just stays there no matter what RPM The truck is at.
My question, is where does it get this tach reference from?
In diagrams I see a tach signal coming off the ignition coil? Is this the wire it gets its info from?
If so, how do I test to make sure that the tach signal is correct or if it is the gauge that is faulty? My manual does not have any information that I can find about diagnosing tachometer problems.
Thanks,
-Chris
I have the OEM tach in the instrument cluster, however when I turn the key to the on position, the tach goes to 500 RPM. When I start the truck, it goes to around 2000RPM and just stays there no matter what RPM The truck is at.
My question, is where does it get this tach reference from?
In diagrams I see a tach signal coming off the ignition coil? Is this the wire it gets its info from?
If so, how do I test to make sure that the tach signal is correct or if it is the gauge that is faulty? My manual does not have any information that I can find about diagnosing tachometer problems.
Thanks,
-Chris
Lead Driver
Joined: Nov 2002
Posts: 9,558
Likes: 44
From: Concord, NC
If your truck is running, then the signal should be correct. The ground on the coil is switched every time a cylinder fires, so the tachometer just keeps track of the frequency that the circuit is grounded and converts that to a revolutions per minute reading. I'm not really sure what, if anything, is between the negative side of the coil and the tach input wire on the instrument cluster.
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