When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey all, I could use some advice on how to investigate/fix my fuel gauge issue. After installing the AAW classic upgrade harness when the ignition is in the “On” position the fuel gauge maxes out, even though I have <1/4 tank of gas. Any help is greatly appreciated.
On the wire from the constant voltage unit, it fluctuates from 11.93-11.99. Nothing on the fuel gauge wire when not connected to the gauge, but when connected to the gauge the voltage on the fuel gauge wire side fluctuates from 7.9 to 8.3.
I wouldn't run it with the nearly full 12 volts coming out of the ICVR for very long. Sounds like it's stuck in the closed position internally. It could harm the gauges if left for too long. Would hate to see that happen.
I wouldn't run it with the nearly full 12 volts coming out of the ICVR for very long. Sounds like it's stuck in the closed position internally. It could harm the gauges if left for too long. Would hate to see that happen.
Thanks for confirming my suspicions. I've been connecting the fuel gauge only to debug it b/c I was worried it might do some damage.
IVR = Instrument Voltage Regulator
also known as
ICVR = Instrument Cluster Voltage Regulator.
It basically takes a 12V type of input and steps it down to the 5V that the gauges want as a maximum and then the sending unit handles from there down.
The video describes a fuel gauge that works opposite of how our fuel gauges work if you are using stock gauges. Some of the stock gauges read low (empty, cold) when disconnected from any source in an open condition or higher ohms like 73 - and read on the high end (full, hot) when there is less resistance like 10 ohms. The more current that flows the higher the gauge will read in those cases. This applies to the Fuel and Temp gauges and Oil Pressure gauge if you have one of those stock, but doesn't apply to the stock Ammeter gauge in terms of it being centered when disconnected.
Thanks all for the information. I have a few more questions.
1) The AAW instructions say to connect the IVR output wire to the Fuel, Temp, and Oil pressure gauges. However, after reading more about the gauges and IVR, I'm getting mixed messages. Should the IVR output connect only to the Fuel and Temp gauges, or should it also be connected to the Oil pressure gauge? BTW, the Oil pressure gauge seems to be working as expected even with the IVR outputting 12v. I've not tested the temp gauge.
2) I plan on purchasing this one https://www.dennis-carpenter.com/tru...er-voltage-reg. How should I bench test it and what am I l checking for?
Last edited by bmaltman2020; Apr 19, 2022 at 08:27 PM.
Reason: There was a response while I was replying that answered a few of my questions.
IVR = Instrument Voltage Regulator
also known as
ICVR = Instrument Cluster Voltage Regulator.
It basically takes a 12V type of input and steps it down to the 5V that the gauges want as a maximum and then the sending unit handles from there down.
The video describes a fuel gauge that works opposite of how our fuel gauges work if you are using stock gauges. Some of the stock gauges read low (empty, cold) when disconnected from any source in an open condition or higher ohms like 73 - and read on the high end (full, hot) when there is less resistance like 10 ohms. The more current that flows the higher the gauge will read in those cases. This applies to the Fuel and Temp gauges and Oil Pressure gauge if you have one of those stock, but doesn't apply to the stock Ammeter gauge in terms of it being centered when disconnected.
Thank you! This is all new to me, so very helpful to know how our trucks with stock gauges work as compared to the video.
To test you'd connect your ground to the housing mounting tab marked in black. Red should be the 12V nominal input and the blue should be 5V output with respect to the same ground. The diagram shows for 1966 F and other series that wire 30 goes to the ICVR and then out to oil, fuel and temp with 31 feeding the back side of the oil pressure gauge for the ground reference through the variable oil pressure sending unit.
As an observer to this info exchange, with continued interest & curiosity, of the seemingly simplistic original factory electrical desgin & engineering of these 'slicks' it goes without saying that the skills required to troubleshoot these systems is broad.
Thank you for sharing that insight on the components, their use and the voltages, ohm specifications and how to troubleshoot, beyond what the numbers simply state (5V, 12V, 0 ohms, 40 ohms, 71 ohms, 90 ohms, etc).
QUESTION: Do the 1961-66 F100 "in-cab" tanks all have the same size tank and same ohm-rated fuel sending unit?
Many thanks again friends - Pete
There were two fuel tanks by number - one was 1961 through 1969 and then 1970 and newer.
C1TZ-9002-H/D0TZ-9002-A
The 1961 through 1965 shop manuals all list the fuel tank capacity as 18 gallons. Then, for 1966, despite using the same tank the shop manual rating changed to 19 1/2 gallons. Not sure why the change but perhaps they started filling it up until it was gushing out and realized they could fit another 1 1/2 gallons if totally topped off so counting the filler neck and any expansion space. Just a hunch, though.
The fuel sending unit likewise had more than one part number over the years.
C1TZ-9725-C/C1TZ-9275-K/D0TZ-9275-A
However, the specified ohms rating remained the same from 73 ohms high resistance when the sender isn't suspended at all to 10 ohms low resistance when suspended by fluid (or by hand) to its maximum travel.
All Ford trucks and cars used King Seeley type gauges up thru the 1970's and perhaps longer. They all work on nominal 5 Volts, and they all operate on 10 ohms high reading and 73 ohms low reading. The car manuals 70,71 & 72 go into great detail on trouble shooting the gauges. These gauges are incredibly sensitive to voltage if the IVR is off by 1/2 volt it will change the readings. When they went to printed circuit instrument clusters, they added an 8.5-ohm resistor in the wire going to the IVR to protect the printed circuit. So, if the IVR failed it would keep it from sending a full 12 volts to the gauges. Grounding a sender wire to see if the gauge is working on the printed circuit type can burn out the printed circuit. We don't have to worry about that but the guys with newer trucks do.
What are the odds. I ordered a new IVR and I'm facing the same issue. There are 12.55v inbound and it's outputting 11.65v. Before returning it, is there anything else I can do or check?
