67 temperature gauge reading backwards

Ausjacko · 12-25-2012, 06:06 PM

I (and a few others) have just finished rebuilding a 67 s-code. I used the original wiring loom. The issue I can’t figure out is why the temperature gauge reads backwards.ffice

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I have installed anew temperature sender and the gauge, at rest, reads below the C. However, at start-up, the gauge swings up to past H and as the car warms-up it moves toward the middle of the dial. When getting hot it moves towards the C. I have checked the connections (a number of times) behind the cluster and they are correct.

For completeness, the fuel and oil gauges work intermittently as well. The earth immediately behind the instrument cluster is connected correctly and I installed an electronic regulator. Any thoughts/help appreciated. I am now quite adept at instrument cluster removal.

rayhicks1969 · 12-25-2012, 06:29 PM

Do you have a ground(earth) from the motor to the firewall?

Boom · 12-25-2012, 07:01 PM

The other gauges not working would make me think a common ground issue. When the others work, do they show levels correctly?

Might be a bad gauge, assembled incorrectly maybe.

bartl · 12-25-2012, 07:23 PM

Try testing the sending unit. It should have high resistance cold and low resistance hot. If it's the opposite, replace it.

GypsyR · 12-25-2012, 09:01 PM

I've run into that with later model Ford oil pressure gauges where the sending unit was mistakenly replaced with a sending unit meant for use with an indicator light. Slightly different circumstances but the exact same symptoms. I's try another (and hopefully correct) gauge sending unit.

88cougargt · 12-25-2012, 09:42 PM

Do you have the wires on the back of the gauge reversed?

-D

Ausjacko · 12-26-2012, 03:19 AM

thanks for the replies.
Yes, I have the motor to firewall ground connected. Will recheck to make sure it is working (reaqd grind back some of the paint)
It is a new sender but like the original one I removed.
The temp gauge works (albeit in reverse) irrespective of whether the other ones are playing or not. I have only seen the oil gauge work once (bugger)
I don't believe switching the wires behind tghe gauge will make any difference as the gauge works on resistance not polarity.
This is really frustrating!

Rudder! · 12-26-2012, 03:45 AM

Wait a tick, you're in Australia right? Isn't everything supposed to run backwards like toilets flushing in the reverse direction compared to us 'above the equator-types'? Just kidding--couldn't resist.
Only help i can offer is pull the gauge and sender out and hook up manually. Put the sending unit in a pan of water and turn the heat up and watch the gauge. Would be handy if you had the old sender too to test the new unit. This should be a two-wire affair.

Two tips: Don't use the wife's best cookware and enjoy a beer at the same time; makes the wait a little easier.

TheRktmn · 12-26-2012, 11:49 AM

Quote:

Originally Posted by GypsyR

I've run into that with later model Ford oil pressure gauges where the sending unit was mistakenly replaced with a sending unit meant for use with an indicator light. Slightly different circumstances but the exact same symptoms. I's try another (and hopefully correct) gauge sending unit.

+1

It is very common for the two types (gauge -v- light) to get mixed up by the parts folks.
Disconnect the wire from the sending unit and put it to ground (preferably through a 10 ohm resistor). If the gauge goes full scale then the gauge and wiring are correct, replace the sending unit.

You didn't use teflon tape or a sealer on the sending unit threads did you? That's a no-no as the gauge needs to ground through the sending unit threads.

88cougargt · 12-26-2012, 12:06 PM

They most definately are polarized. The gauge has a fixed resistance that is in series with the sender resistance. The sender resistance varies causing the current through the gauge to vary. This causes the voltage drop across the fixed resistance to change. All resistance gauges are actually voltage measurements. Even your DMM makes a small precision voltage for measurement.

If you have an old cluster laying around, briefly touch a 9v battery across the terminals. The gauge will start moving. Flipping the battery over will drive it back the other way.

Inside the meter is an adjustable resistor for trimming the fixed value. A length of wire is wound around a core and connected to the adjustable resistor. The needle is attached to the movement of the core. As current flows through the coil it generates a.south pole on one side and a north pole on the other. Reversing the direction will swap the poles. Fixed magnets on either side attract or repel the coil porportional to the current.

Might be worth checking.

-dan

TheRktmn · 12-27-2012, 11:25 AM

Quote:

Originally Posted by 88cougargt

They most definately are polarized. The gauge has a fixed resistance that is in series with the sender resistance. The sender resistance varies causing the current through the gauge to vary. This causes the voltage drop across the fixed resistance to change. All resistance gauges are actually voltage measurements. Even your DMM makes a small precision voltage for measurement.

If you have an old cluster laying around, briefly touch a 9v battery across the terminals. The gauge will start moving. Flipping the battery over will drive it back the other way.

Inside the meter is an adjustable resistor for trimming the fixed value. A length of wire is wound around a core and connected to the adjustable resistor. The needle is attached to the movement of the core. As current flows through the coil it generates a.south pole on one side and a north pole on the other. Reversing the direction will swap the poles. Fixed magnets on either side attract or repel the coil porportional to the current.

Might be worth checking.

-dan

If the gauge in question is an 1968 model gauge then I have to disagree. The '60s and early '70s models are extremely simple and have no adjustable resistor, no magnets, no poles.
The 'movement' consists of a bimetal strip that is heated by 5VDC passing through a wire wrapped around it and going to ground through the sending unit. The sending unit varies the resistance, thus regulating the flow through the wire and the heat produced. The metal strip bows and flattens depending on the heat generated, and moves the needle. The gauge can be connected either way and will still move in the correct direction.
There are high and low range adjustments, but they are physical adjustments that effect the shape of the bow, not electrical adjustments that effect resistance.
The needle movement is fairly slow compared to the newer gauges that are 'driven' by the electrical current and thus respond much faster than the old gauges that need to heat and cool to move the needle.
As a sanity check I did connect both a fuel and temperature gauge from an old ('67) Mustang cluster - they work normally when power and ground are 'reversed'.

88cougargt · 12-27-2012, 11:32 AM

Fudge your probably right and ill have to eat my words. I was thinking of when I coverted my ammeter to a voltmrter. I'm away from my 67 right now but I could swear they behaved like I described. When I get back ill try it and post a video or concede defeat. Probably the latter.

Ausjacko · 12-27-2012, 07:28 PM

now you see how frustrating this is for me...
A problem shared is a problem..still a bloody problem

Ausjacko · 04-14-2013, 06:18 AM

OK, a confession- I figured out the issue and was purely my wiring skills (which should surprise no one who knows me).

What I had done when I made the new look was to connect the oil sender to the water temp gauge and the water sender to the oil gauge. I now realise this is not good AND the senders work in opposites. Water sender starts with high resistance and moves lower as it gets hotter (hence grounding it swings the needle to H). Oil starts with zero resistance and increases with pressure (hence grounding has no impact on the gauge).
Thanks to those who offered a solution and please forgive my dumb wiring skills.