Gas Gauge or Sending unit

[REDROCKER652002]

Just when I thought I was done, here we are back again. OK, so I took the sending unit out of the tank, grounded it and put the ohm meter on it. Works like a charm. Number goes up when I move the arm up, goes down when I move the arm down. Perfect. My son goes to get gas, hook up the connector to the back of the dash, gauge buries at full. No movement at all. I pull the wires and start from the connection at the sending unit, shows a reading of about 75 ohms. Connect that, go to the back of the plug on the dash, that shows the same. I even go as far as to check both the front and the back of each connection at the wire to make sure. I have good readings all the way thru. So, I take out the dash and put in on the bench. Grab a 9v square battery and hook up the positive to the left terminal and the negative to the right terminal of the gauge. Gauge buries itself on the full side. I move one of the aligator clips to the bottom post and it moves to the negative.

OK, now I am getting pissed, so I go back out the the truck. I take an alligator clip and clip it to the wire on the harness and clip the other side to the post that, according to the circuit board, it goes to. i figure I can bypass the circuit board. I take the another clip and clip the other wire from the harness to the post on the gauge. Nothing. I try grounding it, nothing. What am I doing wrong here guys? Is it a bad gauge, bad circuit board? The circuit board is new, so I cannot believe it is bad. Also, I put new washers and nuts on all the posts, could I have screwed something up there. I have checked and am reasonably sure there is readings going into the gauge just no needle movement I am really leaning towards getting a new gauge. My only other thought is that maybe the sending unit is a higher rating unit? I just cannot figure this thing out. Any words of wisdom?

thanks for all who have helped and those that are reading this and thinking just why in the hell did he buy this truck anyway. LOL. I may just trash the whole thing and get a new under bed tank now, but I don't know if that is going to solve my problem.

RR

[randy500]

Forget the 9v battery crap....

Remove the sending unit tan wire
Turn on the ignition, the guage should move to 3 o’clock (if it does, the guage has power and presumably works)

Connect tan wire at sending unit, guage should move to show fuel level

[randy500]

Based on those tests fix the problem

It can be 3 things

1. Power and ground to the guage
2. The guage is bad
3. Signal from sending unit.


You can bench test the guage with a few wires, why haven’t you done that yet?

Power and ground to the guage,
ground to the sending unit metal surface,
sending unit wire to proper terminal on guage....

[HO455]

Originally Posted by HO455

This link may help.

http://67-72chevytrucks.com/vboard/s...d.php?t=640615

Please take the time to read and understand TBone1964's gospel on fuel guages. (Reposted above) Once you do that the help the others have contributed will make more sense.
Plus since electricity ALWAYS takes the path of least resistance you must have the guage isolated from the circuit board when testing it.

Good luck.

[YoungPup1977]

Check the ohms on the resistor on the back of the gauge....

[REDROCKER652002]

Thanks to all who replied. I am a real novice when it comes to electricity, so I am struggling thru. I will try and do the bench test as you all suggested. This is my first project where I am having electrical issues. So, please bear with me.

Thanks.

[REDROCKER652002]

Originally Posted by randy500

Based on those tests fix the problem

It can be 3 things

1. Power and ground to the guage
2. The guage is bad
3. Signal from sending unit.


You can bench test the guage with a few wires, why haven’t you done that yet?

Power and ground to the guage,
ground to the sending unit metal surface,
sending unit wire to proper terminal on guage....

Please excuse my ignorance, but how do I know which terminal gets the power and which one gets the sending unit wire? I am sorry for asking so many dumb questions, but my kid and I are having a hell of a time with all this. My hope is that it is the gauge, as that would be the easiest fix.

Also, I took the gauge out of the cluster, but the ohm meter to the left and right terminals and got a reading of about 91 ohms. Seems the resistor is working, right? Again, sorry for all the stupid questions, but this is my first go at any of this.

thanks again for all the replies.

Dino

[REDROCKER652002]

Originally Posted by HO455

Please take the time to read and understand TBone1964's gospel on fuel guages. (Reposted above) Once you do that the help the others have contributed will make more sense.
Plus since electricity ALWAYS takes the path of least resistance you must have the guage isolated from the circuit board when testing it.

Good luck.

I have read this ad nauseum. LOL. I am not sure what wires go to which terminals on the back of the gauge. I want to try and bench test the gauge to move on, but I am just too stupid to figure out which wires go where. Any help there, in dummy terms, would be most appreciated. LOL.

Thanks, the retard that is Redrocker.

[randy500]

Guage fuel level sensor on left
Power on right
Ground on bottom

[REDROCKER652002]

Originally Posted by randy500

Guage fuel level sensor on left
Power on right
Ground on bottom

Awesome, thank you that is what I was looking for. Now, I will wire things up and see where we go from there. Thanks again to all who replied.

[REDROCKER652002]

For some reason my replies are not posting. Very frustrating.

Gonna try again. So, I hooked up the gauge to the sending unit as mentioned above on the bench and it works perfectly. I used a 9v battery as my power source, no problems, needle moves up and down as I move the float arm up and down. So, I take the gauge out to the truck and plug it in, nothing. The needle pegs past full. So, I use alligator clips and hook it up like it would be using the harness clip. So, what I was trying was to simulate the connection bypassing the circuit board. I used alligator clips from the brown tank wire to the brown wire in the connector. Brown wire in the connector to the post on the gauge where the brown wire would normally be, power wire from the harness connector to the back of the gauge, ground to ground and then grounded the sending unit. Ohm meter works on all connections, just the stupid needle won't move. LOL Help me oh wise ones. I cannot figure out what I am doing wrong. RR

[HO455]

OK if the guage and the float work on the bench. Then in the truck when the guage is hooked correctly to a 12 volt positive power source and the sheet metal housing is hooked to a known good ground and the post for the sender lead is hooked up to the circuit board correctly and the sender is hooked to the brown wire behind the seat and the top of the sender is hooked to a known good ground and the needle goes past full to about the 3 O'clock position you have an open wire between the sender and the guage.

See post #6 in the thread by TBone1964. http://67-72chevytrucks.com/vboard/s...d.php?t=640615

The guage pointing to 3 o'clock means there is no path to ground for the sender post on the back of the gauge. If you hook the your system up on the test bench and disconnect either wire at the sender you will reproduce what is happening in the truck.
As shown in the #6 post the first photo shows the guage reading 3 o'clock with second photo showing the ground wire not connected. The 3rd photo shows the guage reading with the wire at the sender post disconnected as shown in the 4th photo.

Have you verified the gound at the sender is good?

Disconnect the ground wire from the sender. Get a long wire and connect it to the ground wire you just disconnected from the sender (not to the sender itself) and then run the other end near the battery. Hook it to the black lead on your voltmeter and put the red lead on the positive post. Record the voltage. Then measure the battery voltage directly by putting the black lead on the negative post and the red lead on the positive post. They should be the same value. If not then you have a bad ground.
A bad ground will cause resistance and cause the voltage to be lower. The higher the resistance the lower the voltage. For example if your battery voltage is 13.4 and the voltage you measure with your long test lead is 12.8 that is a poor ground and needs to be corrected.
To further prove you have a bad ground use the long test wire you just ran and hook one end to the negative post and hook the other end to the top of the sender. The guage should work and now you have to locate where the bad connection in the ground circuit is. The ground circuit starts at the ground wire to the sender and travel's back through the body and frame to the negative post on the battery.
If your voltage checks are the same then the wiring between the circuit board socket and the sender is broken. You will have to trace the wire to find the break.
Once again you can use your long test wire to test your results. Start by hooking it to the sender (make sure the factory wire is disconnected). Hook up the known good ground wire to the sender top. Hook the other end of the long test wire to the sender post on the guage. Once again make sure the factory wiring is not connected to the guage. Your guage should work.

[randy500]

Im almost positive at one time you posted a picture of the back of your guage panel and the printed circuit wasnt grounded to the metal backing....

For crying out loud post pictures of what your doing.

[randy500]

Great post 455HO
But first he should see if the guage is getting power and ground through the wiring harness and through the printed circuit.
The easiest test for that is to ground the sender terminal at the guage or the fuse panel to see if the guage moves....then troubleshoot the sender circuit.
If the guage doesnt move you dont have power or ground, fix that if needed then move on to the sender circuit.

I ALREADY WROTE THIS ONCE BEFORE, ARE YOU GOING TO EVER DO IT, OR JUST KEEP ASKING QUESTIONS?

[HO455]

Originally Posted by randy500

Great post 455HO
But first he should see if the guage is getting power and ground through the wiring harness and through the printed circuit.
The easiest test for that is to ground the sender terminal at the guage or the fuse panel to see if the guage moves....then troubleshoot the sender circuit.
If the guage doesnt move you dont have power or ground, fix that if needed then move on to the sender circuit.

I ALREADY WROTE THIS ONCE BEFORE, ARE YOU GOING TO EVER DO IT, OR JUST KEEP ASKING QUESTIONS?

Thank you sir.

[REDROCKER652002]

Sorry for being so stupid guys. Just trying to help my son figure this out. It very well could be a ground issue as now nothing in the dash is working. Thanks to all who tried to help.

[REDROCKER652002]

Originally Posted by randy500

Great post 455HO
But first he should see if the guage is getting power and ground through the wiring harness and through the printed circuit.
The easiest test for that is to ground the sender terminal at the guage or the fuse panel to see if the guage moves....then troubleshoot the sender circuit.
If the guage doesnt move you dont have power or ground, fix that if needed then move on to the sender circuit.

I ALREADY WROTE THIS ONCE BEFORE, ARE YOU GOING TO EVER DO IT, OR JUST KEEP ASKING QUESTIONS?

I am sorry, but I thought I did that. When I bench tested it, I ran a power wire from the battery to the power post on the gauge. Ran a wire from the sending unit terminal to the post on the gauge and grounded it all. I got the needle to move then. Am I missing something? Sorry to be so stupid, but I am just trying to help my son out.

[dmjlambert]

I've been following your thread. I suggest don't worry about the gas gauge right now since nothing is working in the dash. Get some of the simpler things working first, like the lights including the 4 illumination lights, turn signal indicators, the brake light during start, and high beam indicator. If you think there is a problem with grounding, attach an alligator test lead between some bare metal of the instrument cluster, and a good clean bare metal area of the dash or firewall. Let's see some pictures of what you have connected.

[LockDoc]

-
There is a factory ground wire from the dash to the cluster connector. Make sure it is connected and making good contact.

LockDoc

[REDROCKER652002]

A finally, hopefully, to this thread as well. In the "I'm a moron" category, I decided to try and dig into this again one day when my son was gone. I pulled the sending unit out, grounded everything and it worked. The gauge moved as I moved the arm on the unit. So, I then touched the flange on the sending unit to the gas tank and moved the float arm, and I'll be damned it moved (no reference to the Seinfeld episode when George got his massage from a male, lol). So, now I am really wondering, so I took the dash panel out and laid it on the seat. Moved the arm and nothing. So, the only thing I can figure is that the dash panel grounds when you screw it in, and that, and a broken float, were my issues all along. I am happy it seems to be working out, but feel like a moron for not realizing it to begin with. Either way, seems to issue with the gas gauge has been resolved.

Thanks to all who had input, and I apologize for being so stupid.

RR

[LockDoc]

Originally Posted by REDROCKER652002

A finally, hopefully, the this thread as well. In the "I'm a moron" category, I decided to try and dig into this again one day when my son was gone. I pulled the sending unit out, grounded everything and it worked. The gauge moved as I moved the arm on the unit. So, I then touched the flange on the sending unit to the gas tank and moved the float arm, and I'll be damned it moved (no reference to the Seinfeld episode when George got his massage from a male, lol). So, now I am really wondering, so I took the dash panel out and laid it on the seat. Moved the arm and nothing. So, the only thing I can figure is that the dash panel grounds when you screw it in, and that, and a broken float, were my issues all along. I am happy it seems to be working out, but feel like a moron for not realizing it to begin with. Either way, seems to issue with the gas gauge has been resolved.

Thanks to all who had input, and I apologize for being so stupid.

RR

Hey, That is the way we all learn. Don't be so hard on yourself. Even the so called "Gurus" have been there done that..

LockDoc

[Getter-Done]

Good Deal










.

[Ol Blue K20]

Originally Posted by LockDoc

Hey, That is the way we all learn. Don't be so hard on yourself. Even the so called "Gurus" have been there done that..

LockDoc

X2, I have made the same mistake multiple times

[REDROCKER652002]

Originally Posted by LockDoc

Hey, That is the way we all learn. Don't be so hard on yourself. Even the so called "Gurus" have been there done that..

LockDoc

Hey, thanks man. I felt kinda stupid, well honestly I felt really stupid. I have been working on my own cars since I was 16, and my dad always said start with the simple stuff. LOL. KISS, *Keep it simple stupid LOL.

[HO455]

Congratulations on solving your dilemma!
And thanks for posting your findings for others to learn from.

HO455