Please read the whole story before replying with common knowledge responses... I am very familiar with how this is supposed to work. But before removing the instrument cluster one more time, I thought I'd see if anyone had an answer to this peculiar situation.
The original problem was the fuel gauge in my Barracuda wasn't working — had never worked in the 40+ years my family had owned the car. But the problem WASN'T the instrument voltage regulator (IVR) integrated into the fuel gauge, because the oil pressure and temperature gauges worked fine.
I eventually got around to pulling the cluster to remedy the problem. I found a lot of the pins in the big round plug were loose. This started a round of soldering, reassembling, testing, removing and re-soldering. Basically, every time I put it back in the car, another pin broke loose (even though I was reinforcing them with brass brads). I finally gave up on that circuit board and found another one on FABO with good solid pins all around.
This time, the fuel gauge actually registered. But after topping off the tank and driving it awhile, I realized something weird was going on — now ALL the gauges were reading at 1/2 the actual value. A full tank read as 1/2 tank. Fully warmed up, the temp gauge was on the first notch — it previously ran right on the 2nd mark. Oil pressure was steady on the 2nd mark — it used to run at the 4th mark.
I know the IVR is supposed to drop the voltage down from 12V to 5V (by intermittently switching on and off). Would it be correct to conclude that it is actually dropping the voltage to approximately 1/2 that value (2.5V) and that that is creating the low readings?
Now, you might ask why the temp and oil gauges weren't reading low before. Well, I had two different fuel gauges on my bench for testing when I reassembled the cluster, and I recall choosing the one that looked better, since they both seem to respond to test voltage. So it's probably the fault of this particular gauge. I'm just curious what the actual mechanico-electrical explanation might be.
The original problem was the fuel gauge in my Barracuda wasn't working — had never worked in the 40+ years my family had owned the car. But the problem WASN'T the instrument voltage regulator (IVR) integrated into the fuel gauge, because the oil pressure and temperature gauges worked fine.
I eventually got around to pulling the cluster to remedy the problem. I found a lot of the pins in the big round plug were loose. This started a round of soldering, reassembling, testing, removing and re-soldering. Basically, every time I put it back in the car, another pin broke loose (even though I was reinforcing them with brass brads). I finally gave up on that circuit board and found another one on FABO with good solid pins all around.
This time, the fuel gauge actually registered. But after topping off the tank and driving it awhile, I realized something weird was going on — now ALL the gauges were reading at 1/2 the actual value. A full tank read as 1/2 tank. Fully warmed up, the temp gauge was on the first notch — it previously ran right on the 2nd mark. Oil pressure was steady on the 2nd mark — it used to run at the 4th mark.
I know the IVR is supposed to drop the voltage down from 12V to 5V (by intermittently switching on and off). Would it be correct to conclude that it is actually dropping the voltage to approximately 1/2 that value (2.5V) and that that is creating the low readings?
Now, you might ask why the temp and oil gauges weren't reading low before. Well, I had two different fuel gauges on my bench for testing when I reassembled the cluster, and I recall choosing the one that looked better, since they both seem to respond to test voltage. So it's probably the fault of this particular gauge. I'm just curious what the actual mechanico-electrical explanation might be.
