Watts to fuel gauge pin at fuse box

[4thgencreamsicle]

I’m trying to get my fuel & temp gauges working. Right now I’m specifically trying to find out how many watts I should have at the fuel gauge pin in the fuse box. Mine reads right at 8 with the key on.

’69 sbc, original gauge cluster.

Additional info: Fuel gauge sits at empty. The sending unit wire pegs out the gauge @3 oclock position when grounded. I haven’t taken out the sending unit in the tank to test the float situation. The tank, unit and float are all new, but I get that new doesn’t always mean working. I just don’t have the ability to have my truck down for long (I have chronic pain, so everything we do over here takes significantly longer than the average person especially when I’d have to pull the seat). I’ve replaced the printed circuit and thought I had cleaned up the pins on the wiring, but will hit those again this week just in case. Trying to get new resistors for the back of the gauges and hope that does the trick, but checking what I can for the time being.

The truck came to me with the wrong temp sender so we fixed that and cleaned up the wiring (previously melted). It reads cold but when grounded and the key on it pegs out to high. Otherwise it just stays at cold.

Neither of these have ever worked for us.

I’m working through the thread by Tbone as I can but since both are out I am doubting it’s just a bad float at the gas tank.

[RustyPile]

The gauge response you get when grounding those leads indicate the circuits, for the most part, are complete and working.. As for the temp gauge, I suspect you have the wrong sending unit or it's not making electrical contact through the threads where it screws into the engine. Never use Teflon tape or similar on the threads. It sounds like you have a sending unit for a light instead of a gauge..

The same conclusion applies to the tank unit.. Either the float has sunk or stuck near the bottom. Also possible the tank unit doesn't have a good ground path back to the battery.. A "quick and dirty method" to check this is to make up a long jumper wire with alligator clips on each end. make the jumper long enough to reach from the battery to the tank and sending unit. Attach the jumper tp the metal body of the sending unit, not the wire terminal post. The tank grounds to the cab through the mounting bolts.. The cab grounds to the frame through ground straps located between the cab and frame. Be sure the ground strap located at the rear of the cylinder head on the passenger side and a bolt attaching the heater/AC case to the body.

None of these tests nor access to the fuel sending unit require removing the seat. Simply sliding the seat fully forward provides access..

Also, I'm curious.. Watt is a unit of electrical power. Voltage multiplied by amperage yields wattage. Explain the method you used to measure the power consumed by the fuel gauge circuit. And why do you feel it necessary to measure wattage?

[4thgencreamsicle]

Originally Posted by RustyPile

The gauge response you get when grounding those leads indicate the circuits, for the most part, are complete and working.. As for the temp gauge, I suspect you have the wrong sending unit or it's not making electrical contact through the threads where it screws into the engine. Never use Teflon tape or similar on the threads. It sounds like you have a sending unit for a light instead of a gauge..

The same conclusion applies to the tank unit.. Either the float has sunk or stuck near the bottom. Also possible the tank unit doesn't have a good ground path back to the battery.. A "quick and dirty method" to check this is to make up a long jumper wire with alligator clips on each end. make the jumper long enough to reach from the battery to the tank and sending unit. Attach the jumper tp the metal body of the sending unit, not the wire terminal post. The tank grounds to the cab through the mounting bolts.. The cab grounds to the frame through ground straps located between the cab and frame. Be sure the ground strap located at the rear of the cylinder head on the passenger side and a bolt attaching the heater/AC case to the body.

None of these tests nor access to the fuel sending unit require removing the seat. Simply sliding the seat fully forward provides access..

Also, I'm curious.. Watt is a unit of electrical power. Voltage multiplied by amperage yields wattage. Explain the method you used to measure the power consumed by the fuel gauge circuit. And why do you feel it necessary to measure wattage?

I’ll be looking into these tips this week. Thanks. The temp sending unit is for the gauges. It used to have the temp sender for light so we fixed that. I knew about no Teflon tape, but my hubby was the one that actually installed the new sender…I wonder if he used some! I’ll definitely look into that.

Ugh. I meant volts. 8 volts.

I cleaned up the existing grounds and where they made connections a couple weeks ago because of the other threads. I was hoping it would help. All the original ground locations were there including the one you mentioned, but only a few actually connected. Fixed that and I even added a couple. But I can easily try a test wire, we have everything I’d need to do that. Thanks.

As far as just sliding the seat forward, I have the original seats (build sheets were still in the back when I recovered them), but even with my seat slid all the way forward I can barely fit my small hand behind there to remove the sending unit wire off the post. Weird. Still, removing the seat is free to do, so if the temporary ground to my tank doesn’t help, I will just have to do it and pull the sender. You mentioned I might have the wrong sending unit. I’ll have to look back through my orders to know exactly which one I got, but which one am I supposed to have?

Updated that I was able to look and we bought the tank and sender from Brother’s Trucks sender is part# GTSU108.

[RustyPile]

In case you don't know how the temperature sending unit works, I'll explain.. The sending unit for the warning light is a simple off-on temperature sensitive switch.. During cold to normal coolant situations, the switch is off. When the temperature reaches abnormally high temperatures, the switch turns on, providing a ground path for the light. If there are no faults in the circuit,, the light turns on...

For a temperature gauge, the operation is totally different. The sending unit is a temperature sensitive variable resistor.. With coolant temperature changes, the resistance through the sending unit changes. This change in resistance causes the gauge needle to rise and/or fall.. The lower the temperature, the higher the resistance.. When you ground the lead, the resistance is very low (near 0 ohms) and the guage goes to "hot". When a sender for lights is in place for a gauge, the needle will "sit" on cold until the engine is an actual state of overheated. Like I originally stated, either your sending unit is for a light, or it's not properly grounding through the threads. A third possibility is the sending unit is defective. The sending unit, whether for a light or gauge is easy to check..

Testing a "light" sender: Using a DVM, connect the test leads across the unit - 1 lead to the terminal, and the other to the housing. Select "continuity" on the DVM. At room temperature, there will be no continuity (open circuit)..

Testing a gauge sending unit: Connect the test leads as before. Select resistance "auto range" on the DVM.. You should see some resistance on the meter. The actual reading will depend on the ambient temperature.. As a further test, Leave the leads connected, and place the sending unit in a pan of water. Heat the water on a stove. As the water temperature rises, you'll se a change in resistance reading.

I don't suspect a problem with the fuel gauge circuit, gauge, or sending unit. If you have an extra known good fuel sending unit, it's easy to test everything.. Make up a short jumper as I explained. Disconnect the tan wire at the tank and connect it to the test unit post. Connect the jumper between the sending unit frame and the tank.. Turn on the key and slowly swing the float arm through it's range of travel, while watching the fuel gauge needle.. If the needle follows the sending unit arm, everything in the dash and also the tan wire is functioning as they should.. This means one of two things.. You said the needle stays on empty, so either the tank is actually empty or the sending unit is defective.

I offer this for what it may be worth to you.. I've bought from Brothers in the past and have had problems with their customer service and product quality.. I no longer do business with them.. Classic Industries is my choice of suppliers for original reproduction parts. Here's a link to the proper coolant sending unit from Classic Industries..

https://www.classicindustries.com/pr...ts/748691.html

[pjmoreland]

Originally Posted by 4thgencreamsicle

Additional info: Fuel gauge sits at empty. The sending unit wire pegs out the gauge @3 oclock position when grounded

I'm confused by these results. Is there any chance it was actually the other way around? Normally the fuel gauge will go to empty when the tan wire is grounded, and 3 o'clock when disconnected.

[RustyPile]

Originally Posted by pjmoreland

I'm confused by these results. Is there any chance it was actually the other way around? Normally the fuel gauge will go to empty when the tan wire is grounded, and 3 o'clock when disconnected.

By Jove, you're right.. Last week, I was in and out of the hospital taking all manner of medical tests and have been pretty bushed. Plus I haven't been able to sleep much. I typed all that stuff in the middle of the night. I should have caught that but I didn't.. Thanks pjmoreland, for pointing that out. I'm sure that's the case..

[4thgencreamsicle]

Originally Posted by RustyPile

By Jove, you're right.. Last week, I was in and out of the hospital taking all manner of medical tests and have been pretty bushed. Plus I haven't been able to sleep much. I typed all that stuff in the middle of the night. I should have caught that but I didn't.. Thanks pjmoreland, for pointing that out. I'm sure that's the case..

You’re both right! Note to self: Don’t post when your on pain pills. Lol. Okay, so I really feel like deleting this thread because of all the confusion I have caused, but y’all are super helpful. The tan wire, disconnected rises the fuel gauge to the 3 o’clock position and goes back to E when grounded. I just wrote it out wrong.

So far this morning I have cleaned off the Teflon tape from the temp gauge and we’ll see what happens when I run all my errands today. It is the right button too temp sender I think we even bought it from classic industries.

Gas tank situation will have to wait for the moment as I gotta get a kid to work this morning.

Seriously guys, thanks so much for taking the time!

[RustyPile]

Originally Posted by 4thgencreamsicle

You’re both right! Note to self: Don’t post when your on pain pills. Lol. Okay, so I really feel like deleting this thread because of all the confusion I have caused, but y’all are super helpful. The tan wire, disconnected rises the fuel gauge to the 3 o’clock position and goes back to E when grounded. I just wrote it out wrong.

So far this morning I have cleaned off the Teflon tape from the temp gauge and we’ll see what happens when I run all my errands today. It is the right button too temp sender I think we even bought it from classic industries.

Gas tank situation will have to wait for the moment as I gotta get a kid to work this morning.

Seriously guys, thanks so much for taking the time!

No... Don't delete your thread.. pjmoreland and I can get you through this just fine on this thread.

While you have the temp sensor at hand, run a test to be sure you have the correct sensor. This test can be done with it installed, and the engine at room temperature. Using a DVM set to read 1K - 2K ohms. With the engine not running, connect one test lead to the base of the sender and connect the other lead to the "button". If you have the correct sender you should read some amount of resistance. The actual value will vary with actual temperature of the sender. If your DVM indicates infinity or "open circuit", switch the DVM to read continuity. If you still get a reading of "open circuit", you definitely have the wrong sender. Remember-- the sender for a light is a simple off-on temperature sender. It's "off" until the engine is in an overheat state.

[4thgencreamsicle]

Originally Posted by RustyPile

No... Don't delete your thread.. pjmoreland and I can get you through this just fine on this thread.

While you have the temp sensor at hand, run a test to be sure you have the correct sensor. This test can be done with it installed, and the engine at room temperature. Using a DVM set to read 1K - 2K ohms. With the engine not running, connect one test lead to the base of the sender and connect the other lead to the "button". If you have the correct sender you should read some amount of resistance. The actual value will vary with actual temperature of the sender. If your DVM indicates infinity or "open circuit", switch the DVM to read continuity. If you still get a reading of "open circuit", you definitely have the wrong sender. Remember-- the sender for a light is a simple off-on temperature sender. It's "off" until the engine is in an overheat state.

Ok I took a pic so you can make sure I have it on the right setting. I know it’s not located in the ideal place but I haven’t been able to get one turned down to fit in original placement by the plugs. Still, once the thermostat opens up I should be getting some at least some sort of reading at the gauge, right?

Also, I got the brilliant idea of using our endoscope camera (bought when we lost a brass plug in a different engine). This thing comes in clutch. Well I figured I could look in the tank and see the float situation…accidentally submerged the camera and wouldn’t you know, the float is sunk to the bottom. Not exactly the way I was hoping to inspect things, but hey, it DID work. 😬 I have a new float ordered already. We’ll obviously go ahead and test the sender when it’s out. Just to be sure.

[RustyPile]

Originally Posted by 4thgencreamsicle

Ok I took a pic so you can make sure I have it on the right setting. I know it’s not located in the ideal place but I haven’t been able to get one turned down to fit in original placement by the plugs. Still, once the thermostat opens up I should be getting some at least some sort of reading at the gauge, right?

Also, I got the brilliant idea of using our endoscope camera (bought when we lost a brass plug in a different engine). This thing comes in clutch. Well I figured I could look in the tank and see the float situation…accidentally submerged the camera and wouldn’t you know, the float is sunk to the bottom. Not exactly the way I was hoping to inspect things, but hey, it DID work. 😬 I have a new float ordered already. We’ll obviously go ahead and test the sender when it’s out. Just to be sure.

By looking at your picture, I can't tell exactly where your sensor is located.. The important thing is that the sensor be located in the water passage below the thermostat..

pjmoreland and I have been discussing your project.. We've both come to the conclusion that your float is sunk, and your camera verified that.. I've come across a few of these reproduction fuel sending units that have a crack in the solder joint. Install a new sending unit and 2 - 3 days later the float is sunk.. Here's what I've come up with.. The loop at the end of the arm where the float is connected is too small. It squeezes the float too tight and cause the solder joint to fail.. I open the loop a bit so that the flat stays in place, yet will rotate when given a slight twist. If you would like I can share with you a method that tests the sending unit while it's still mounted in the tank.. I'll be glad to give the explanation through this site's messaging feature..

[4thgencreamsicle]

Originally Posted by RustyPile

By looking at your picture, I can't tell exactly where your sensor is located.. The important thing is that the sensor be located in the water passage below the thermostat..

pjmoreland and I have been discussing your project.. We've both come to the conclusion that your float is sunk, and your camera verified that.. I've come across a few of these reproduction fuel sending units that have a crack in the solder joint. Install a new sending unit and 2 - 3 days later the float is sunk.. Here's what I've come up with.. The loop at the end of the arm where the float is connected is too small. It squeezes the float too tight and cause the solder joint to fail.. I open the loop a bit so that the flat stays in place, yet will rotate when given a slight twist. If you would like I can share with you a method that tests the sending unit while it's still mounted in the tank.. I'll be glad to give the explanation through this site's messaging feature..

That makes sense because we installed the sender before the truck was ready to go so it would have had time to sink before I ever say the gauge work. Go ahead and send me a pm. 😎

[pjmoreland]

I have a couple of questions about your 564-Ohm measurement of the temperature sender:

1) Did you have the truck harness wire disconnected from the sender when you took this measurement?

2) Where was the black lead of the multimeter touching?

[RustyPile]

I think you said you may have bought the fuel sending unit from Classic Industries?? If so, you can contact them and explain what happened, they'll send a replacement.

BTW, Brothers sells the same sender for both V8 and I6 and suggests using an adaptor.. The adaptor throws the fuel line alignment off and is a general PITA to get hooked up.. Another reason I quit dealing with them... Classic Industries offers both sending units..

[4thgencreamsicle]

Originally Posted by pjmoreland

I have a couple of questions about your 564-Ohm measurement of the temperature sender:

1) Did you have the truck harness wire disconnected from the sender when you took this measurement?

2) Where was the black lead of the multimeter touching?

The sender wire was disconnected and the black lead was at the base, red on the button.

[4thgencreamsicle]

Originally Posted by RustyPile

By looking at your picture, I can't tell exactly where your sensor is located.. The important thing is that the sensor be located in the water passage below the thermostat..

pjmoreland and I have been discussing your project.. We've both come to the conclusion that your float is sunk, and your camera verified that.. I've come across a few of these reproduction fuel sending units that have a crack in the solder joint. Install a new sending unit and 2 - 3 days later the float is sunk.. Here's what I've come up with.. The loop at the end of the arm where the float is connected is too small. It squeezes the float too tight and cause the solder joint to fail.. I open the loop a bit so that the flat stays in place, yet will rotate when given a slight twist. If you would like I can share with you a method that tests the sending unit while it's still mounted in the tank.. I'll be glad to give the explanation through this site's messaging feature..

That makes sense because we installed the sender before the truck was ready to go so it would have had time to sink before I ever say the gauge work. Go ahead and send me a pm. 😎

[4thgencreamsicle]

Here’s an update! Life got in the way and we had to wait on looking into all of this. Then a couple of days ago part of my ignition wiring burned up when I tried to start the truck. Because that’s how life works, we apparently aren’t allowed to have enough running vehicles in our driveway to keep all 4 of us on the road. Lol.

I was able to unbolt the seat today and slide the whole seat forward in the cab. I’m small so there was enough room for me to be able to work behind the seat. Pulled the sending unit out and sure enough the float was full of gas. Replaced it and got everything back in. Turned the key to the on position and smiled big as the gauge crept up to just under a full tank… beautiful!!!!

I still gotta see what’s up with the temp sender, but while pulling the wire harness apart to free the burned ignition wires, we found a old sketchy splice in the sender wire that we’ll fix because it was all sorts of corroded. Then we can see how things go.

Big thanks for the help!!! Even if my truck isn’t running right now and wants to burn to the ground, I will at least know how much gas is in the tank to fuel the fire. 🤷😂