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Problems installing tacho

Discussion in 'VT - VX Holden Commodore (1997 - 2002)' started by Cannman07, Jan 17, 2020.

  1. Cannman07

    Cannman07 New Member

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    Hey, I've had a small tacho for about a year that I hooked up myself and it works fine. I bought a bigger one (3.5"), same brand, SAAS, and it wires up the same way but I couldn't get a review signal. It lights up, remembers the colour it was on but the needle won't move. Thought it was faulty so I took it back and exchanged it for another of the same model but it's just the same. I've hooked my smaller tacho back up and that's working fine. Any ideas on what it can be? I've read the threads but can't find anything relating to this exact problem of the smaller one working but the bigger one won't.
     
  2. accentstencil

    accentstencil Well-Known Member

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    Any extra wires on the bigger one? Did it come with wiring diagram?
     
  3. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    [​IMG]
    Is this the one.
     
  4. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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  5. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    So By these 2 the wire positions are different so know wounder its not working.
     
  6. Cannman07

    Cannman07 New Member

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    Almost, there's no orange one. Green is always the rev signal.
     
  7. Cannman07

    Cannman07 New Member

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    Yep, this is the wiring for the small one that works.
     
  8. Cannman07

    Cannman07 New Member

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    No, the bigger one has one less wire. It came with a wiring diagram.
     
  9. ant797

    ant797 Active Member

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    Your meant to install the tacho at the top front not the bottom behind a barrito might fit better from the bottom
     
  10. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    Well if you tell us the model it would help, but if you go off the old one colours and put them in order to your new one then it will work, u cant just use the harness even though it fits, using a small pression screw driver remove the pins and put them in the correct order.
     
  11. Cannman07

    Cannman07 New Member

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    It in a VX series 2 V6 manual. The wiring diagram for the SAAS 95MM Tacho is red wire to switched 12v, black wire to ground, green wire to rpm signal and white wire to battery for LED memory. The wiring for the small SAAS Tacho is the same but for some reason it has an extra orange wire to connect to battery for LED memory. I've got lights and power on the big tacho, the needle jumps up when the power is turned on but the rpm needle doesn't move after that. The green wire is definitely hooked up to a rpm signal because it's the same wire I use for the green wire on the small tacho so I'm confused as to why it won't get a rpm signal.
     
  12. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    But what harness plug are you using? The order which they plug into wont be the same if your using the old plug for your 52mm, also the SAAS model which IS it be good saying its 95mm which is 3.75" not the 3.5" which is 90mm ?
     
  13. Cannman07

    Cannman07 New Member

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    Sorry for the confusion, both tachos have their own separate wiring harnesses. The plugs in the back of the tachos are completely different. The big one is 95mm and the little 52mm. But they wire up the same apart from the 52 mm having the extra orange wire as I explained above.
     
  14. ant797

    ant797 Active Member

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    maybe you have confused the 12v battery orange wire car side for the ignition wire car side try connecting the wire you used for the 12v battery on smaller tacho to the ignition wire on bigger tacho
     
  15. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    Well I think I worked it out for you, the white wire goes to +12v constant power not the illumination like the old one.
     
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  16. Cannman07

    Cannman07 New Member

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    Thanks for your help too
    Thanks, I'll have a go wiring up the big one tomorrow and see how I go.
     
  17. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    Your welcome his the link, Note the white wire to battery + = constant power. If you turn your lights on then it will work with your set up as long as its not on dim.
    https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=2ahUKEwjYieeso4znAhVPyjgGHbdZAIMQFjAPegQIARAB&url=https://www.shopsaas.com/assets/files/install/MuscleTachLargeFitting.pdf&usg=AOvVaw00jb8JPrCFwnYu_p1zRm3h
     
    Last edited: Jan 18, 2020
  18. Cannman07

    Cannman07 New Member

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    Had a go hooking it up today, followed your instructions with the white wire and still no luck. I have power to the unit, lights and the function button works to set the revs for the shift light but no rev signal. I've got the green wire (rpm) connected to the rpm signal wire at the back of the instrument cluster, I know it's the signal wire because it works with the other tacho using the green wire for rpm. I'm stumped.
     
  19. Trevor loves holden.

    Trevor loves holden. Well-Known Member

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    This maybe the issue as they use 5v on commodore, its in the installation guide,
    Problem: “ECU tach output is only 5volts”
    - If the tach output from your vehicles ECU is only 5volts, a 10K 1/4 watt resistor is needed to increase the signal voltage to 12volts. (Nissan, Subaru, Etc..)
    Installing a resistor: Connect one side of the resistor to the green signal wire of the tacho and connect the other side of the resistor to the red 12volt ignition wire of the tacho. Do not cut any wires, just splice into.
    WARNING: Do not connect the resistor to any other wire or you WILL damage the tacho and your ECU!
    -
     
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  20. Cannman07

    Cannman07 New Member

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