Edited: another fuel/temp gauge thread, but turns out the harness is melted together

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hotrod swinger

hotrod swinger

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1973 Swinger

After owning my car for 12 years, I finally have power to all of my gauges and warning lights. But the gauges aren’t functioning properly.

Presently the temperature gauge reads low even when the engine is at normal/high operating temperature.

The fuel gauge reads full when the tank is full, but reads empty when there are still 40 litres in the tank.

Where do I start to correct this problem?
 
Have you replaced the sender for either gauge?

Could be the IVR is putting out low voltage?

Could be a bad ground to the gauges

Could be high resistance in the bulkhead connectors

Could be high resistance in the cir board.
 
1973 Swinger

Presently the temperature gauge reads low even when the engine is at normal/high operating temperature.

The fuel gauge reads full when the tank is full, but reads empty when there are still 40 litres in the tank.

Where do I start to correct this problem?
 
Volt ohm meter to temp sender wire to ground. At the sender end. Should see approximately 5 volts dc fluctuating. Digital meter may not pick it up. If that’s good try a temporary ground to metal part of instrument cluster. I’d personally try the ground anyway.
 
You need to think of this as an "end to end" problem

The cluster gets power thorugh the key switch, but is it "correct?" In other words does a voltage drop cause problems?

The cluster connector pins are/ can be a problem, they were crimped/ riveted to the pc board traces. Clean and solder them, and check the harness connector

The gauge regulator / limiter/ IVR may be/ gone/ going bad. Get a modern solid state one like from RTE

The IVR contact fingers in the pc board may not be making contact with the board. Solder jumpers across

The gauge studs / nuts may be corroded where they contact the pc board. Twist the nuts loose/ tight several times to clean and tighten connections

The gauges may be damaged/ out of cal/ bad. Test them using test resistors

Again to the cluster connector pins, the sender connection pins at the connector may be loose, see above--solder them, and check the harness connector

The temp/ oil (if used) goes through the bulkhead. Check those terminals

The fuel goes through the rear harness/ kick panel connector. Check that connector

All senders have a wire end terminal, which can be loose/ corroded

The senders can be bad/ out of cal, or poor grounding to the sender at the tank

:

There are hundreds of threads on this board about testing and fixing gauge problems:

67dart273, gauge tester - Google Search

CHECK CALIBRATION with resistors:

Bench Testing a gauge cluster

c-3826-jpg-jpg.jpg
 
I will pull the cluster and check all of those connections.

Would a missing/disconnected fuel tank ground strap cause these readings?

How do I test whether the correct amount of power is reaching the gauge cluster?

I understand that the cluster is powered by G5 which is a dark blue wire that connects to the printed circuit board and powers the gauges and warning lights:

C8E18C45-9AE5-4E2F-BFFE-D33544914ADE.jpeg
 
Dubob said:
Volt ohm meter to temp sender wire to ground. At the sender end. Should see approximately 5 volts dc fluctuating. Digital meter may not pick it up. If that’s good try a temporary ground to metal part of instrument cluster. I’d personally try the ground anyway.
Click to expand...
^^^ This is a good place to start^^^^

Page 8-48 in your FSM
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upload_2022-1-15_21-9-2.png


If it passes that, then go on to the next checks
 
You may have more than one issue. Your fuel gage acts like what happens when you replace the tank sender with an aftermarket unit. If the original sender has been replaced with an aftermarket version, they are very different than the original, and the gage will not work properly.

If that is your problem, you have two basic options:
1. Get an oem style sender
2. Get a device called a Meter Match that can be programmed to match the aftermarket sender to the fuel gauge.
 
hotrod swinger said:
I understand that the cluster is powered by G5 which is a dark blue wire that connects to the printed circuit board and powers the gauges and warning lights:
Click to expand...
So if the brake warning light works, then there is some power available.
Since the fuel sender moves, there must be some power flowing through the IVR to the gage and the sender back to ground.

Yes there should be a ground connector that clips to the sender and fuel line.

Here's how the gages and senders work.
Thermal-Electric Gauges (Session 227) 1966 Master Technician's Service Conference 10

The filmstrip that goes with that
 
Checked the voltage at the temp sensor connector. Fluctuates between 0 and 5 volts with the key in the run position.
 
Resistance at temperature sender:
Almost entirely cooled: 110
Normal operating temperature: 24

I replaced my fuel sending unit a few years ago, and with an aftermarket gauge it read full when full and ready empty with 12 litres of fuel in the tank. I’ll test to see how much fuel I add when the stock gauge reads empty.
 
Last edited:
When I ground the oil sender connector the warning light comes on when I turn the key (I don’t have the stock sending unit yet, just an aftermarket sender).

Also, the resistance at the aftermarket sender with the car idling is around 110 and with the engine not running is 10. Can I use the aftermarket sender or should I replace it with a stock sender?
 
Last edited:
I must say, I’m really stoked to get my stock cluster working. I’ve been putting it off for years, just seemed really intimidating with all of the different variables.
 
hotrod swinger said:
Almost entirely cooled: 110
Normal operating temperature: 24
Click to expand...
c-3826-jpg-jpg-jpg.jpg

So the gage should have read near the middle whe nthe engine was hot. Right?
And the cold end of the scale will be off.

hotrod swinger said:
I replaced my fuel sending unit a few years ago, and with an aftermarket gauge it read full when full and ready empty with 12 litres of fuel in the tank. With my stock gauge it reads full when full and empty with 40 litres in the tank.
Click to expand...
They've got to be matched units. Plus the float arm and its resistance need to be calibrated for the arc and the tank shape.
 
Mattax said:
So the gage should have read near the middle whe nthe engine was hot. Right?
And the cold end of the scale will be off.
Click to expand...

unfortunately no, at normal operating temperature the gauge was reading very low.
 
hotrod swinger said:
When I ground the oil sender connector the warning light comes on when I turn the key (I don’t have the stock sending unit yet, just an aftermarket sender).

Also, the resistance at the aftermarket sender with the car idling is around 110 and with the engine not running is 10. Can I use the aftermarket sender or should I replace it with a stock sender?
Click to expand...
The resistance of the sender sounds like an oil pressure sender and not an oil lamp sender. If it is quite large, IE about 2" dia x 2" or more long it is an oil GAUGE sender and not a "lamp" sender. A lamp sender should be a dead short to ground with engine off, and open with engine operating. "It's a switch"
 
Post 4 shows a graph of various senders and what MY gauge needs, resistance wise, to read correctly.

Product Review: A100 Fuel Sender For 67 Dart

When your tank has 40L (about 10 gallons) the sender should have about 20 to 25 ohms. When empty it should be in the 70 to 80 ohms.

It is posable that your gauges are damaged, I recently had my IVR fail and it pegged the temp and fuel gauges. Fuel seems to have survived but the temp reads off the chart low when the key is off and 1/2 way between cold and the first line of normal when at normal operating temp. (It used to be a few degrees to the right of the first line of the normal range)

Notice post 25, damaged gauge...

The gauge failure posts cursed my car
 
hotrod swinger said:
Can you get these at regular auto parts stores?

Can I have a make and part number?
Click to expand...
Last I knew you could get the oil and temp senders, but not fuel, let me clarify........you are trying to get the oil light to work, right? If so, you should be able to just look it up by year/ model application of your vehicle.

Only fuel senders is (ask others here) there are a few folks rebuilding OEM ones (yours) otherwise "try" to find a "new old stock" OEM, and good luck with that. All the repops are inaccurate.
 
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