Temp sending unit question

Discussion in 'Ranchero Tech Help' started by jonnie, Jul 22, 2020.

  1. jonnie

    jonnie In Second Gear

    Messages:
    44
    Hi again,
    As you all helped me work out, my 65 has a 80’s 302 fitted, it also had a horrid wooden dash affair that I’ve removed & replaced with an original type dash. The problem is that the temp gauge doesn’t work, I know the gauge itself is ok & the sensor on the engine worked the old gauge. I know the gauges I’ve fitted are 9 volt & was wondering if the 80’s sensor is 12 volt which could be my problem? I’ve seen two different sensors for sale one for engines after jan 65 & one for before.. my truck was build dec 64 & registered jan 65 so I’m right on the cusp! Any help would be appreciated...
    cheers,
    Jonnie
     

    Attached Files:

  2. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

    Messages:
    3,056
    Location:
    Portland OR
    The 9 volt sounds incorrect; any '65-up US car should be 12 volt.
     
  3. jonnie

    jonnie In Second Gear

    Messages:
    44
    That’s what I’m saying, mine was built in Dec 64 but registered in Jan 65. The instruments fitted are from a 65 mustang I think & have the little voltage regulator on the back..
     
  4. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

    Messages:
    3,056
    Location:
    Portland OR
    Mine was built Dec. 9, 1964 and registered as a '65 also, and all the electrics are 12 volt.
     
  5. jonnie

    jonnie In Second Gear

    Messages:
    44
    Maybe I’ve put the wrong dash in then I take it yours doesn’t have the regulator on the back of the clocks ?
     
  6. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

    Messages:
    3,056
    Location:
    Portland OR
    I have the exact same dash bezel (early Mustang) as you, with the standard instrument voltage regulator. I transferred my original Ranchero gauge cluster over to it, a direct swap. Still, nothing should be 9 volts, unless possibly the regulator is failing, a pretty common problem.

    There's a new solid state version of that regulator available.

    Sprint wheel.JPG Screen Shot 2020-07-22 at 1.41.25 PM.png
     
  7. jonnie

    jonnie In Second Gear

    Messages:
    44
    That’s interesting & my mistake for thinking 9 volts as I bought that regulator from them with a new bezel & fuel sender unit, they’re great & very helpful company. I’m still confused as to why the sensor in my engine wont operate the gauge, the gauge works fine if I earth the feed wire, which is what makes me think it must be the sensor!
     
  8. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

    Messages:
    3,056
    Location:
    Portland OR
    I don't believe there's anything else in that circuit, so it could be the sensor, or possibly a ground (earthing) issue somewhere. Have you checked for a ground wire behind the passenger cylinder head to the firewall?

    Yes, falconparts is a great company, my go-to for anything Falcon related.
     
  9. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    11,488
    Location:
    Seguin, TX
    OK, quick diagnosis time. But first, aren't the gauges (except fuel) 5 volts, and the IVR 5 volts? Anywhoo, to test gauge, turn ignition on, remove sender wire and ground it. If the gauge works, the needle will go full deflection (to hot).
     
  10. beerbelly

    beerbelly In Maximum Overdrive SILVER MEMBER

    Messages:
    3,056
    Location:
    Portland OR
    Andy's right- the regulator output is 5 volts, but the car's electrical system is 12 volts.
     
  11. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    11,488
    Location:
    Seguin, TX
    I was making sure FoMoCo didn't have something different.
     
  12. jonnie

    jonnie In Second Gear

    Messages:
    44
    Thanks for the replies, If I earth the wire the gauge works, do you think my problem may be that the 80’s sender might be 12 volt?
     
  13. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,862
    Location:
    Chesapeake, VA
    Do you have the ground wire from the back of the engine block to the firewall and are the connections clean?

    Did you use a thread sealant such as teflon tape or a RTV type substance when installing the sending unit?

    Suggestion: replace the sending unit with the correct Ford Motorcraft sending unit.
     
  14. jonnie

    jonnie In Second Gear

    Messages:
    44
    The company here in the UK lists two different units one for pre & one for pre 9/1/65 & one for after but with my engine being a 1987 302 I’m not sure which unit I need? If they both work at 5 volts I guess I buy the later one..
     
  15. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,862
    Location:
    Chesapeake, VA
    The temperature sender drives the gauge/instrument, the engine year isn't the determining factor in this case, and if it is pre 9/1/65 then you need the earlier one. FWIW.
     
    The Wrench likes this.
  16. jonnie

    jonnie In Second Gear

    Messages:
    44
    Thank you for the advice, I’ll order one now..
     
  17. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,862
    Location:
    Chesapeake, VA
    Ensure you have a ground wire from the back of the engine to the firewall. All manner of random instrument readings/failure to register occur if that wire is absent or the connection is disrupted or intermittent.
     
    pmrphil, beerbelly and The Wrench like this.
  18. jonnie

    jonnie In Second Gear

    Messages:
    44
    Thank you, I’ll check that out..
     
  19. 65restomod

    65restomod In Overdrive BRONZE MEMBER

    Messages:
    820
    Location:
    Danville,VT left NJ forever
    Just a little add on- to ensure the cluster and gauges continue to work it may be worth running a secondary separate ground from the ground (earth ) point by the steering column to the VR hold down screw, ( fixed my problem)
    I used a quick disconnect crimp spade connectors making it easy to remove cluster without getting behind VR to remove the screw.
     
  20. jonnie

    jonnie In Second Gear

    Messages:
    44
    Thanks for all the help & advice, new earlier type sensor fitted today & all working fine.
     

Share This Page