Hey guys, I just dealt with this issue just 1 month ago.... not that I am expert/nor electrically adapt, but it is easy to go around and around on this, which of course, I did. In the end, I had a old sending unit/float, bad wires (or grounding), and a faulty gauge. I bought the new sending unit from Classic Industries to ensure the type was correct for car. Also, the 62/63 shop
manual talks about the types of faults and that the gauge type is "floating". Therein, there are gauge 'floating' symptoms and gauge 'indicates full' symptoms. The incorrect sending unit type/oms
is not talked about as its assumed 'you get the right one'.
I recommend to check to ensure its compatible with your car. Here is the one,
Sending Unit, to check against as I bought it and installed, it works.
Importantly, I experienced both 'symptoms' from 'floating' and 'indicates full'. I thought the same that 'the sending unit was of wrong type'... it was correct type. I also thought to test the oms or to manually move the float to judge full/empty. But the manual does not suggest this, it basically says: if its 'floating' its a wiring issue, if it 'indicates full' its a short, if reading is incorrect its the sending unit. (yes, just replace the old unit and it threw me as, isn't a short a wiring issue?
)
I think here, we talking about a 'floating' symptom. I also
started with a floating gauge and also that it somewhat indicated something. So, 'some' reading is not a good path to solving in my opinion, again, just ensure the part is correct (!). After that, the manual says: When the key is 'on' and the gauge 'floats', it seemed to say "this is a wiring issue" which I tackled.
Here is what I did,
A. Symptom 'floating' gauge with key 'on'.
1. Replaced the old tank sending unit
2. Replaced the wires
3. Cleaned grounding contact (near tank)
3.1. Tested ground by connecting to Neg battery terminal directly with a long wire. (test failed, but was just to ensure the non-functioning gauge was not result of bad sending unit grounding)
B Symptom changed to 'indicates full' with key 'on' (normally wired with new sending unit)
--- I was a bit confused as "what else is there?" ---- 1. Sending Unit (check), 2. Wiring (check). 3. The Gauge itself (?).
4. Pulled Instrument Cluster
5. Removed fuel gauge (
very carefully - the resistor is wire coiled and exposed -
here is the same type but not the same gauge as Nova). if broken, that is expensive, but my thinking was 'its broken already'
6. Disconnect the parts,
very carefully, clean with copper brush. Clean very sensitive parts
with only a small amount of spray cleaner. (I used electrical spray cleaner)
7. Reassemble Gauge into Instrument Cluster
8. Clean Instrument Cluster grounding
9. Lean the Cluster into place and test.
Cleaning the gauge itself worked for me,
works perfectly. Old Gauges can be the issue. Most times guys replace the entire instrument cluster. The fuel gauge seems 'solid state' so the contacts (screws, nuts and copper contacts) were old and dirty. Brushed clean and spray cleaning the rest (very carefully!).
.02