RPM's don't work
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Freshman User
Joined: Jan 2021
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RPM's don't work
Hello I have a 1985 F250 with a 7.5L. I have been having a problem with my RPM's not working. I am not sure what could be making this happen I have checked and fixed the circuit board on the back of the instrument panel so I know it is not related to the electrical or the traces on the back of the instrument panel . Does anyone else have any idea what else cold be casing my RPM's not to work? Thank you for any suggestions!
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
With the Duraspark ignition system, there should be connectors on the inner fender on the driver's side. One will have a green colored wire coming from the coil. This provides the electrical signal for the tachometer. Check for looseness or damaged wires.
There is a connector with two black [I think] wires which provide the two necessary grounds for a V8 engine. Six cylinder engines just have one ground for the tachometer.
On the back of the tachometer are 4 terminals: "B" = battery [12 volts]; "C" = coil [green wire from the coil]; "G" = ground [for 6 & 8 cylinders; "8" = 2nd ground for V8 engines only.
With the tachometer removed [for testing], connect jumper wires to the appropriate places and see if the tachometer works.
Be very careful regarding moving engine parts while testing.
There is a connector with two black [I think] wires which provide the two necessary grounds for a V8 engine. Six cylinder engines just have one ground for the tachometer.
On the back of the tachometer are 4 terminals: "B" = battery [12 volts]; "C" = coil [green wire from the coil]; "G" = ground [for 6 & 8 cylinders; "8" = 2nd ground for V8 engines only.
With the tachometer removed [for testing], connect jumper wires to the appropriate places and see if the tachometer works.
Be very careful regarding moving engine parts while testing.
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