Help with Temp, Gas, Oil Alt gauges FREE VIDEO INCLUDED!

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It could still be a poor ground back at the sending unit. More resistance will cause the gauge to read low.
L = 73.7 Ohms
M = 23.0 Ohms
H = 10.2 Ohms
M would be 1/2 a tank of gas.

Here's the strap that grounds the sending unit. If you haven't checked, make sure you have one. 1966 Dodge Coronet Sending Units | OER K-MF290

strap.jpg
 
I couldn't find the picture I took of mine, but here's one from Allpar. The strap bridges over the short rubber fuel hose at the gas tank. You should be able to slide underneath the gas tank and look up and see it. It faces the front of the vehicle.

In the photo you can also see where the sending unit electrical wire connects. That the wire that runs to the gauge in the dash. As the sending unit rises and falls, the resistance in the sending unit wire changes the resistance to the gauge and moves the needle accordingly.


sending unit.jpg
 
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That ground jumper isn't the only player. The fuel line is attached to the chassis with several steel clips. But even if the line and all those clips are rusted bad there should be sufficient accumulative ground path. Then the jumper between firewall and engine block is a player also.
To throw a edumacated guess as to why the fuel gauge needle doesn't quite reach the full mark when there is a full tank?... The inside of the fuel gauge looks about the same as the temp gauge. The crusty crud buildup on the beam/winding restricts beam/needle movement. Whatever the original fault was, it blistered the copper trace off the circuit board. It could have damaged both gauges.
Here's a brain teaser... How did the defective temp gauge pass 2.43 volts? That was shown in a previous pic.
 
RedFish said:
That ground jumper isn't the only player. The fuel line is attached to the chassis with several steel clips. But even if the line and all those clips are rusted bad there should be sufficient accumulative ground path. Then the jumper between firewall and engine block is a player also.
To throw a edumacated guess as to why the fuel gauge needle doesn't quite reach the full mark when there is a full tank?... The inside of the fuel gauge looks about the same as the temp gauge. The crusty crud buildup on the beam/winding restricts beam/needle movement. Whatever the original fault was, it blistered the copper trace off the circuit board. It could have damaged both gauges.
Here's a brain teaser... How did the defective temp gauge pass 2.43 volts? That was shown in a previous pic.
Click to expand...
Yeah hmm, where was that voltage coming from..., because the temp gauge wires were completely unattached inside. So how was the current running thru. Just btw, was 2.43 volts a proper reading from the tip of the temp sensor? Im gonna order another gauge if I can find one on ebay
 
RedFish said:
That ground jumper isn't the only player. The fuel line is attached to the chassis with several steel clips. But even if the line and all those clips are rusted bad there should be sufficient accumulative ground path. Then the jumper between firewall and engine block is a player also.
To throw a edumacated guess as to why the fuel gauge needle doesn't quite reach the full mark when there is a full tank?... The inside of the fuel gauge looks about the same as the temp gauge. The crusty crud buildup on the beam/winding restricts beam/needle movement. Whatever the original fault was, it blistered the copper trace off the circuit board. It could have damaged both gauges.
Here's a brain teaser... How did the defective temp gauge pass 2.43 volts? That was shown in a previous pic.
Click to expand...
Okay well, it looks like there isn't any type of ground strap on the unit, that i can see and a possible "fix" on the wire to the sending unit it self. Also would this rusted up nut that keeps the gas tank be an issue for grounding as well?

20180316_171014.jpg


20180316_170955.jpg


20180316_170923.jpg
 
The tank may be chassis grounded, rusty or not. The issue isn't the tank but the sender. A chassis ground path from sender to tank is questionable due to a seal/gasket between there. Then the rubber fuel hose also isolates sender.
Since the strap supporting the tank has or should have a rubber isolator between it and the tank, along with a insulating pad atop the tank, and a rubber seal at the filler tube, chassis ground at the tank is questionable. So that's why there isn't a male spade terminal made on the tank and a length of common wire from sender to the tank. A simple clip on ground jumper was installed from sender fuel tube to vehicles fuel line. Those other options were just too "iffy" .
There may be a OEM type ground clip available. Some owners have homemade a ground jumper using a length of wire, attached to the senders fuel tube with additional gear screw clamp, and at other end a ring terminal under a sheet metal screw placed in the vehicles chassis under there somewhere.
Right this minute your sender is grounded to the tank at that clamp ring and the tank is chassis grounded. This is shown/proven in gauge operation. Is there a 2 or 3 ohm resistance present that is effecting gauge accuracy? I don't know. Your ohms meter between sender face plate and vehicle chassis answers that question.
 
RedFish said:
The tank may be chassis grounded, rusty or not. The issue isn't the tank but the sender. A chassis ground path from sender to tank is questionable due to a seal/gasket between there. Then the rubber fuel hose also isolates sender.
Since the strap supporting the tank has or should have a rubber isolator between it and the tank, along with a insulating pad atop the tank, and a rubber seal at the filler tube, chassis ground at the tank is questionable. So that's why there isn't a male spade terminal made on the tank and a length of common wire from sender to the tank. A simple clip on ground jumper was installed from sender fuel tube to vehicles fuel line. Those other options were just too "iffy" .
There may be a OEM type ground clip available. Some owners have homemade a ground jumper using a length of wire, attached to the senders fuel tube with additional gear screw clamp, and at other end a ring terminal under a sheet metal screw placed in the vehicles chassis under there somewhere.
Right this minute your sender is grounded to the tank at that clamp ring and the tank is chassis grounded. This is shown/proven in gauge operation. Is there a 2 or 3 ohm resistance present that is effecting gauge accuracy? I don't know. Your ohms meter between sender face plate and vehicle chassis answers that question.
Click to expand...
 
So i bought and installed this NOS temp gauge from Brads Parts. The gauge itself seems to work, even though the needle was a tad bent upwards, i tried to fix that, but it still seems "stuck" .....It looks like it wants to pin all the way and then settle back down.
 
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