Fuel/Water Temp Gauge Issue Found! Now what...

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Righty Tighty

Righty Tighty

Blame it on the dog
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So, neither my fuel gauge nor the water temp gauge was working when I bought my 71 Scamp. I tried a new fuel sender to troubleshoot, no change. Today I removed the instrument cluster to get to the bottom of it, and saw a broken piece of circuitry leading to the fuel/water temp gauges. I don't know what the circuitry part is called, if anyone knows please chime in.

Anyway, I'm almost certain this is what caused the issue. My question is, how do I fix it? Can this be soldered? My guess as to what caused it is maybe a bare wire somewhere touched it and shorted.
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That will do it every time! You could find try to find another board or just scrape the coating off the circuit on each side of the break and solder a jumper wire in.
Also remove or reattach that part that’s came loose from the board.
 
Easy fix as cudascott said.
Just clean both sides of the brake and use a small bit of wire to bridge the gap. Tin both sides of the trace and both ends of the wire before you solder it all back together.

You can also buy a reproduction cir board.

Lastly make sure you cluster has a IVR (voltage regulator) installed and working.
 
Don't stop there. More work to be done, you can fix it

I think this is the old thread on board repair, but the photophhphphphucket has crapped on the photos

Printed circuit pins repair

General idea:

Harness connector pins. Clean them and solder the pins to the board traces

Solder jumpers across the spring clips that make contact with the IVR. The fingers lose contact with the board traces

Loosen/ tighten the gauge stud nuts several times as they get corroded

Add a ground pigtail to a ground point on the board and bolt the other end to a ground such as column support.

Buy yourself a solid state replacement for the IVR

Use big eraser to buff clean the copper where the bulb sockets contact, and be sure the spring contacts are in good shape and clean

BE CAREFUL!!! DISCONNECT the battery!!! The BIG BLACK and BIG RED ammeter wires are both always HOT!! They are NOT fused

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NOTICE!! THE ABOVE ARE NOT MY PHOTOS THEY came from the 'lost thread' with the lost photobucket photos
 
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In your first pic on the right the rectangular box is the IVR. This is a points type unit with a heated bimetal spring. It opens and closes continuously with ignition on to drop your 12V electrical down to 6V to run the fuel level, water temp and oil pressure gages. You can buy yourself a solid state IVR for about $25 as a plug n play and be done with it, or make one if your electronically inclined for about $5. Heres a schematic below. I have built these up for both my 67 and my sons 69. Nice evening workbench project.

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Also solder the pins to the copper tracings, and on the back sides of the pins where they are hollow, after 50 years this stuff tends to get loose. I cut down small brass coated brads that I got at lowes and glued them inside the pins from the side where the pins are crimped over with super glue. This helps prevent the pins from loosening and coming apart from the board. When doing this make sure theres still clearance between the heads of the brads and the metal gage housing since that metal housing is a ground point. You can file the heads of the brads flatter, or clearance the back of the cluster housing.
 
Heres a pic of a homemade Solid State IVR on my rallye dash. On rallye dashes the IVR is inside the gas gage and must be disabled leaving the gage portion to work. On a dart or any non rallye dash, you would use male spade connectors and plug in at stock location. Note the dielectric grease under the chip, and chips mounting tab is also a ground. Chip will take up to 35 VDC and reduce it to 5.5 VDC so asking it to drop 13.5 VDC to 5.5 isnt asking much of it.

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What we're seeing is the copper trace serving as a fusible link. The root cause is guesswork. Good luck with it.
 
moparmat2000 said:
You can buy yourself a solid state IVR for about $25

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Funny you mention the solid state, prior to removing the cluster I had been reading up on troubleshooting the fuel/temp gauge failure. Seems the most common failure is the voltage regulator, and since it wasn't my fuel sender or a bad ground, that was my next plan of attack. I found some solid state IVRs and it seemed like a good retrofit, and you mentioning it just confirms that it's a good way to go.

RedFish said:
What we're seeing is the copper trace serving as a fusible link. The root cause is guesswork. Good luck with it.
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Agreed. The wiring behind the cluster didn't seem too bad, but I guess all it takes is one bare wire or piece of metal to short it. Unless there was a power surge somewhere that a fuse didn't catch?
 
Prior to 1972 model 12 volt supply to inst' panel/instrument voltage limiter wasn't fused other then the main fusible link outside the bulkhead connection.
 
So, I'm bringing back my old thread here since I'm still working on the problem. I thought I had solved the problem by soldering the damaged circuit and replacing the voltage limiter with a new RTE limiter, but the fuel gauge still didn't work. I thought maybe my solder repair wasn't sufficient, so I found a deal on a new circuit board. Still had the problem.

I bench tested the gauge, gauge is good. I tested the voltage limiter alongside the old limiter for resistance, found the new one had about 13 ohms, while the old one had close to zero. Now, I don't know much about electrical troubleshooting, so I put the old one back in to see what would happen. The fuel gauge needle moved, albeit just a tiny bit. Fuel tank is full.

So, could it be I have a bad sender and that's why the gauge isn't moving all the way to full?
 
Unplug the the gas gage sender wire at the gas tank. Then jump the sender wire directly to chassis ground, and turn the ignition key to the run position. If gas gage goes to full, your gage and wiring are good, and your sender unit is bad. It's really as simple as that. You can test your factory water temp and oil pressure gages exactly the same way. Do not leave the key on longer than you have to with it ground shorted like this. Only to test gage deflection.

If gage needle doesnt move at all then you have other issues either with gage or wiring. Sender wire shorted to ground and everything else being good, the needle will go all the way to the high end.
 
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Pull the sender and inspect it first. There are some common failures including broken resistance wire on the unit. Also a sunk float is the most common cause of the gauge moving a little with the tank full. Make sure the sending unit is well-grounded, too.
 
Glad to help you out. These cars are very simple, dont overthink them. Oil pressure, water temp, and fuel level are all simple variable resistors. Think like your dimmer on your house lighting in maybe your dining room etc.
 
Jim Lusk said:
Pull the sender and inspect it first. There are some common failures including broken resistance wire on the unit. Also a sunk float is the most common cause of the gauge moving a little with the tank full. Make sure the sending unit is well-grounded, too.
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Thanks for the advice. I’ll double check the ground on the sending unit and certainly will pull it for inspection.
 
The sending unit grounds to the metal fuel line. The metal fuel line grounds to the body with the metal fuel line mounting clips. Plenty of areas for grounding failure because of corrosion after 50 years. There is also a clip that jumpers over the rubber fuel line to connect the sender unit to the metal chassis fuel line. If you dont have this jumper clip installed, then you have no ground from the sending unit. Make sure you have this installed and a good ground from the sending unit body through this clip and fuel line to ground to test everything before pulling just the sending unit and ruling that as the cause.

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If you have a factory unit definitly try to fix it. The after market ones don't read as well as the originals. Some members have their originals rebuilt.
 
I removed the sending unit and inspected it. Found the float to have 2 large cracks, and obviously it was filled with gas.
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Naturally, my Tacoma, which is my daily, decided to scrap the throttle position sensor. Of course the TPS is 2 days away, and so is the fuel sender for the Scamp.

Plan B: Run the fuel sender minus the damaged float.

Of course, the tank is leaking like a sieve at the bung, and not one but two people have pointed this out to me. No matter, as long as I can make it to work tomorrow.
 
There is a Ford fuel sender float that is supposed to be the same thing (on a later model). Might be able to find it.
 
If you want your original rebuilt, try Wolf & Co. A good friend sent his there, it came back 100% & works great.
 
Since meter match units have doubled in price now, it probably make sense to rebuild an original if you have that option.
 
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