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Temp and Fuel Gauge don't work
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    Posted: Aug/31/2023 at 6:48pm
Ok, I think this has been mentioned before there a company that makes a solid state Instrument Cluster Voltage regulators . Seems mopars have this problem also. Some  mopars used the ICVR that AMCs use use along with some Fords Mustangs I believe for one. The company is real time engineering 
:  https://www.rt-eng.com/index.php/IVR4_Limiter_List.html . The IVR4 works in a lot of AMCs per there list. I have one in my 1974 Matador coupe and works well. A little bit more expensive then the point type ICVR but not by much and the old point type you never know what your getting china junk or some that been rusting on shelf for 50 years. LRDaum
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Points: 19672 		Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Aug/15/2023 at 8:02pm
Yeah, letting the smoke out is bad!! The IVR quickly switches on and off, faster than a turn signal blinker (sort of like the blinker when a bulb is burned out). You really shouldn't be able to clearly see the on and off points, just a jumping needle (analog gauge) or fluctuating reading on a digital gauge, but shouldn't go over 12V much under 5V -- just bouncing between the two. 

6PakBee calls it a "heater", and that's about right. It's a bi-metal strip that heats and cools rapidly, which causes it to flick on and off rapidly. With all that movement it's easy to see how it wears out and breaks (or sometimes slows down, or sticks open or closed) over a period of 30-50 years!
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Points: 5457 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Aug/14/2023 at 9:14am
From what you describe, you are putting 12v to the gauge and grounding the sensor lead.  Doing this never energizes the IVR heater and you'll have a constant 12v going to the gauge.  This is a crude drawing of what I THINK is the gauge wiring.  If you are trying to bench test the gauge, apply 12v to the gauge and ground the gauge case.  Nothing else.  You should see the IVR functioning and you should have the pulsating voltage at the sensor connection. 


Roger Gazur
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I'm back to thinking it's the IVR, but it's hard for me to know why it's bad. When I bring the gauge over to me bench and hook 12v to it, I expect the contact point to move quickly, switching from 12v to 0v. It does not do that. It'll peg the gauge, heating the wire to point of smoke...which I assume is bad. The contact element point never bends away from the 12v contact point. Strange as it appears to switch from 12v to 0v at the sensor side when in the car.

I don't mind getting aftermarket gauges (I've ordered them already), but I have a hard time giving up not knowing exactly what's wrong with the current setup. I'm to the point now where I'm just going to say it's a bad IVR and move on.
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Make sure the instrument cluster is well grounded. You might need to run an additional ground wire from anywhere on the cluster there is a ground to somewhere metal under the dash. The temp sender grounds to the block. Make sure you didn't use teflon tape or sealer on it! The gas tank grounds to the body through the top of the tank where it contacts the bottom of the trunk floor. That rusts a little and messes up the ground. I always clean the fuel outlet nipple and solder a wire around it, running that wire to the body nearby, grounding the sending unit. This eliminates a bad ground through the tank.
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Points: 5457 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Aug/12/2023 at 5:03pm
Originally posted by tunes12 tunes12 wrote:

Originally posted by 6PakBee 6PakBee wrote:

Simplest test for a functioning IVR is to measure the voltage at the temperature sensor with the key on.  If everything is functioning, the voltage will fluctuate from +12V to 0v about two times a second.  This gives an average voltage of about 5v to the gauges. 


Just tested this. While I do have a digital multimeter that makes it difficult to confirm exactly 0-12v with that fast a speed, I do see it fluctuating to 12v+ and back down to 0v with a regular cyclical pattern. Still no functioning gauge though.


Use a test light.  But it seems your IVR is functioning.  Thermal gauges are fed by the IVR and then are connected to the sensor.  If you have voltage at the temperature sensor but yet the gauge doesn't work, you either have a bad gauge or a bad sensor.  The voltage at the sensor has to go through the gauge.  
Roger Gazur
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1970 Sonic Silver auto AMX

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Originally posted by tunes12 tunes12 wrote:

Next, when I ground the temp gauge wire at the sensor to the block, it pegs the temp gauge, as I believe it should. When I ground the sender wire at the fuel tank, the fuel gauge also pegs.
This verifies the IVR is working, as are the sense wires. 

Both gauges are rated 9Ω full scale, and 75Ω for the low end reading. 

650 - 1kΩ in the fuel sensor means you will never register on the gauge. It sounds like you may have to pull the sensor from the tank and have a closer look.

The resistance of the temp sensor can also be measured. The TSM has instructions on this. Soaking it in boiling water (the sensor, not the TSM) should produce around 9Ω resistance.

Originally posted by tunes12 tunes12 wrote:

While I do have a digital multimeter that makes it difficult to confirm exactly 0-12v with that fast a speed, I do see it fluctuating to 12v+ and back down to 0v with a regular cyclical pattern.
That's exactly what you should see. The switching rate of the IVR is too slow for the meter, so the reading wanders whether on VDC or VAC setting.
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Points: 6875 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Aug/12/2023 at 8:47am
If you have power, maybe you don't have ground.
Try taking the cover off the gauge cluster and running a wire from the cluster housing to the temperature gauge body and then a clean spot on the fuel tank.
If the gauges work, then you know you have ground issues somewhere between battery, gauge cluster, chassis, engine and fuel tank.
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Originally posted by 6PakBee 6PakBee wrote:

Simplest test for a functioning IVR is to measure the voltage at the temperature sensor with the key on.  If everything is functioning, the voltage will fluctuate from +12V to 0v about two times a second.  This gives an average voltage of about 5v to the gauges. 


Just tested this. While I do have a digital multimeter that makes it difficult to confirm exactly 0-12v with that fast a speed, I do see it fluctuating to 12v+ and back down to 0v with a regular cyclical pattern. Still no functioning gauge though.
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Points: 5457 		Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Aug/12/2023 at 7:56am
Simplest test for a functioning IVR is to measure the voltage at the temperature sensor with the key on.  If everything is functioning, the voltage will fluctuate from +12V to 0v about two times a second.  This gives an average voltage of about 5v to the gauges. 
Roger Gazur
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1970 Sonic Silver auto AMX

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