Temp not working on instument panel

[Gene]

The temp isn't working on my "new" 68 1/2 cab. I checked the sensor with an ohm meter and it reads open. I get constant voltage from the plug to ground and seem to remember reading something about it either supposed to be constant or pulsing? (Need to find my ford manual) Isn't there some kind of voltage regulator or something on the back of the instrument panel? I replaced the sensor with another one from a parts engine and it got burned out too, (now reads open with the ohmmeter and before it didn't). If I can't find the manual can anyone point me in the right direction? I seem to remember also something about checking the instrument readout with a resistor? anyway
I'll take voltage readings and post them tomorrow. Any help will be appreciated.
Thanks!

 

[Viperwolf1]

The instrument voltage regulator (IVR) is on the back of the gauge cluster and it does pulse. It also supplies current to the fuel level and oil pressure gauges. If those gauges are working then the IVR is not your problem. You can substitute a 10 ohm resistor for the sender to give you a high temp reading and a 73 ohm resistor for low temp reading.

 

[Gene]

I found the shop manual after getting home. You are correct with the above statement. On my truck, the voltage reads 12.8 volts with the engine running on the wire to the temp sender unit. But it does not pulse, unless my digital volt meter doesn't pick it up. All the other gauges work with the exception of the temp. I put a 10ohm resistor in there between the sensor wire and ground but the temp gauge still doesn't work. I have a few spare instrument panels so may swap temp gauges to see what happens.

 

[65 mustang]

Take the wire off temp sender. Ground the wire to metal. With key on the gage should move,if not the gage is bad. Scott

 

[70_Steve]

I On my truck, the voltage reads 12.8 volts with the engine running on the wire to the temp sender unit. But it does not pulse, unless my digital volt meter doesn't pick it up. All the other gauges work with the exception of the temp.

I suspect the gauge is not the problem. Use your digital to check the wire to the oil pressure sending unit. On the 20 VDC range, the digital meter should show random numbers between .5 and around 10.5 volts. If you measure a constant 12.8 volts, something is hosed up in the wiring harness.

Here's a site I use for my schematics. Might come in handy trying to track down this problem.
http://www.wsu.edu:8080/~i6735189/

 

[Viperwolf1]

I suspect the gauge is not the problem. Use your digital to check the wire to the oil pressure sending unit. On the 20 VDC range, the digital meter should show random numbers between .5 and around 10.5 volts. If you measure a constant 12.8 volts, something is hosed up in the wiring harness.

Here's a site I use for my schematics. Might come in handy trying to track down this problem.
http://www.wsu.edu:8080/~i6735189/

X2, not the gauge or the IVR. Something is wrong in the wiring. The temp gauge power is jumpered from the the oil pressure gauge. Make sure someone didn't change it to switched battery power.

 

[Gene]

I will check the wiring further, But I know it is correct between the temp sensor back to the gauge. I'll go back further and post back here.

 

[70_Steve]

I will check the wiring further, But I know it is correct between the temp sensor back to the gauge. I'll go back further and post back here.

Not much left to check. With the IVR being mounted on the back of the instrument cluster, there's only about 6" of wire to jumper between gauges. Viperwolf1's diagram shows the oil pressure an water temp gauges being jumpered together. I remember two or three of my gauges being jumpered like that.

 

[Gene]

I suspect the gauge is not the problem. Use your digital to check the wire to the oil pressure sending unit. On the 20 VDC range, the digital meter should show random numbers between .5 and around 10.5 volts. If you measure a constant 12.8 volts, something is hosed up in the wiring harness.

Here's a site I use for my schematics. Might come in handy trying to track down this problem.
http://www.wsu.edu:8080/~i6735189/

I get a constant 12.8 volts in and out of the I.V.R. , through both sides of the gauge, all the way to the temp sensor connector at the end of the wire.

According to the schematic the input to the IVR ties into the wire which comes from the Keyswitch which has the same voltage 12.8 volts. This is correct on my truck. What does the IVR supposed to do, Limit the voltage to something less than 12 volts (according to the quoted reply above)? If so then the IVR is the problem, right? I had a good temp sensor but after installing it it got burned out (open).
Thanks!

 

[Viperwolf1]

That would be a bad or ungrounded IVR. It turns on and off by way of a thermal switch. The output should average 5V over a period of time. After you change it be prepared for the oil pressure and fuel level gauges to read about 1/3 to 1/2 of what they were reading. Temp sender is bad if it reads open.

 

[70_Steve]

What does the IVR supposed to do, Limit the voltage to something less than 12 volts (according to the quoted reply above)? If so then the IVR is the problem, right?

The Instrument Voltage Regulator (IVR) is actually miss-named. It's really a current regulator. It does this by pulsing the CD voltage, using a bimetalic strip to operate a set of contacts, similar to the turn signal or emergency flasher, but much faster. I need to appologize because, for some reason, I assumed that your oil pressure and fuel level gauges were working... Yes, replace the IVR.

Edit:

All the other gauges work with the exception of the temp.

OK. So I reread the posts and found this statement. Not sure how the stock oil pressure and fuel level could work if the IVR is not working... The ammeter is on a different circuit.

 

[Gene]

Thats what i don't understand either, The oil pressure works fine and it reads 12v at the sensor just like the temp sensor wire. When I crank the truck the oil press goes up to around 40psi. Also I verified that the IVR is grounded.

I changed the IVR with another used one and have the same issue, so I guess it is bad. I do have another one but will have to dig it out of the other parts truck.

Anybody have a part number for a brand new IVR from autozone, dimmicks, napa, etc..?

Sometimes the people looking up the parts are not to good at their job but that is another post for another time.

Thanks.

 

[70_Steve]

Thats what i don't understand either, The oil pressure works fine and it reads 12v at the sensor just like the temp sensor wire. When I crank the truck the oil press goes up to around 40psi. Also I verified that the IVR is grounded.

Hmmm.... We are talking about the stock gauges, aren't we??:?

 

[Gene]

yep they are stock.

I am just going to buy another IVR and temp sensor and see what happens.

 

[70_Steve]

I am just going to buy another IVR and temp sensor and see what happens.

Before you throw more parts at it, you might want to really find out what the problem is. From the wiring diagram Viperwolf1 provided (or at the link I provided) you can see that the wiring is pretty simple. It should not be a big task to trace the wires from the IVR to the gauge, and from the gauge to the sending unit. Also, unhook the IVR, turn on the key and make sure you don't have 12 volts on any of those wires...