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Thread: Speedhut speedo issue
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03-12-2020 #1Registered User
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- Jul 2017
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- Nashville, TN
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Speedhut speedo issue
I have 1978 Firebird with a GM LS3 Connect and Cruise setup. All of my gauges seem to be working well with the exception of the electric (non gps) Speedhut Speedometer. I have a VSS sensor feeding the ECU and I have the Vehicle speed out wire from the bulkhead connector setup as the speedo signal wire and the ground is the vss ground. When I start the car the speedo jumps to 20mph and the odometer is moving. I have hooked up HP tuners and I can see the ECU does not show any MPH from the ECU. I have things setup the way Speedhut says with the step down resistor between a 12v switched source and the signal wire. Am I doing something wrong here? I don't believe calibrating will fix the issue because it is obviously getting signal at rest. Thanks in advance.
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03-12-2020 #2Registered User
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- Jul 2006
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- El Paso, Texas
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I checked both manuals and there is no resistor wired in the circuit. Only the tach uses that setup. You should have a straight connection from the bulkhead to the speed input wire. Which ground are you referring to? Some of the Speedhut speedos have two wires, one signal and one ground. In those cases the wires can connect direct to the sender but if you're using the ECM you would only use the signal wire. I attached some links from Speedhut and the GM instructions. HTH.
Alex
Vehicle Speed (BROWN) – This is a non scaled output for use with
auto-scaling speedometers and will not function unless a vehicle
speed sensor (VSS) is connected to the ECM through the VSS wire
in the harness.
https://www.speedhut.com/instruction..._338_4_412.pdf
https://www.speedhut.com/instruction...tructions1.pdf
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03-12-2020 #3Registered User
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- Jul 2017
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- Nashville, TN
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I have two yellow wires, 1 yellow red(signal) 1Yellow Black (ground)
So currently I am setup as the optional setup provided in the first link you have listed. In this scenario the gauge is getting the signal from the ecu/brown wire from bulkhead. When using the ecu the instructions to use a 12v switched power and a 4.7k to 10k .25 ohm resistor to tie into the signal wire. The yellow black should be grounded (currently that is grounded.
Because the brown wire in the bulkhead is not scaled does that mean I can run the bulkhead brown wire directly to the yellow red(signal) wire and don’t need the resistor and 12v accessory in place?
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03-12-2020 #4Registered User
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- Jul 2006
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- El Paso, Texas
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It must be something new as far as hooking up the speedo. I've never seen it done like that. I would say run it without the resistor and 12v connection and see what it does. I doubt you would fry anything.
Alex
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03-13-2020 #5