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speedo just sits at 10 mph

Discussion in 'Chevy C/K Truck Forum' started by 88k2500, Jan 25, 2014.

  1. 88k2500

    88k2500 Member

    I have seen a few threads about speedos but none seem to be same as my issue. Mine just sits at 10 mph and doesnt move. Shut truck off and still the same thing. The wiring from sensor seems to be good. The dash is that odd one without the needles if that makes any since. I was also wondering if anyone has used a secondary pump in line for the fuel in order to bypass the factory one. I took the engine computer and all that out and now I run a carbed 350.
  2. the phantom

    the phantom Active Member 2 Years ROTM Winner Gold Member 1000 Posts

    Welcome to the club fellow NY'er!!! I cant remember what causes them spedos to quit working but I remember the style your talking about. they have like a different color from the background indicating speed fuel ect. I think. Im sure someone will chime in with a possible cause. Hope you figure it out and stay warm... gonna be a tid bit chilly next week..:great:
  3. 88k2500

    88k2500 Member

    I have been told that there are 2 wires that went to the pcm that when grounded will make the speedo work but I have yet to able to verify that.
  4. DrumBound

    DrumBound Member

    They are the moon style gauges. Could be that your speedometer is bad. I'll have to look at the one I have, but I'm pretty sure these are sensor driven and not mechanically driven. So if the wire that sends the data to your speedo has a break in it or you're not getting proper power to it then it will not give a reading at all and will just be stuck in position. Gimme an hour or two and I will check on some diagnostics for it.

    Check if you computer is sending a signal to the instrument cluster. I wish I could tell you which wires it was, but havent got that far into it yet. If it is just sitting at ten constantly then it is getting power. Otherwise it would bounce around with the motion of the truck. So just ensure that it is getting a signal from the computer. Another likely culprit it the circuit board. Test your guage with a 12v power supply. Top and bottom posts are positive and negative. The supply between 1-8v to your left and right posts, if it moves then the guage isn't the issue. Sorry if I am causing more problems then solutions. Hope it helps.
    Last edited: Jan 26, 2014
  5. 88k2500

    88k2500 Member

    there in lyes the issue, the computer is not connected. It no longer has computer control. So its carburated with no electronics on the motor and trans except for the speed sensor and the essential warning light/gauge wiring
  6. DrumBound

    DrumBound Member

    Do you still have the wiring for the computer installed?Even if there is no comouter control the sensors can be tricked into believing the computer is still plugged in. Also, there should be a red probe coming out of the fuel pump relay. That is a hot wire directly to the fuel pump. So if you attach a 12v power supply to it, that you decide how to control, it will operate the fuel pump.
  7. 88k2500

    88k2500 Member

    I wired a 30 amp relay to the fuel pump control and power wires from the ecm. The wiring is still in there from the computer and I have tested them but I cant figure out what wires have anything to do with the speedo. It would be nice to be able to have that working. Someone told me that there are two wires in there that can be grounded together and that will make the speedo function but I have no clue how true that is or what wires are involved and I have been looking for this info for a long time.
  8. DrumBound

    DrumBound Member

    Have you tried running your speed sensor directly to your speed sensor?
  9. 88k2500

    88k2500 Member

    What? Running my speed sensor directly to my speed sensor? From what I can see the wires from the speed sensor in the t case run to the cluster..
  10. DrumBound

    DrumBound Member

    Sorry about that. Running your speed sensor directly to your speedometer. If you remove the cluster you can remove the left and right connecting tabs and connect your speed sensor directly to your speedometer with butt connectors

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