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Discussion Starter · #1 ·
I posted a while ago but still was unable to solve the problem. I replaced the sending unit in my 65 chevelle. When I filled up the tank it read about 1/4. I tested the new sending unit and it is working correctly. When I pull the brown wire from the sending unit the guage reads full. That means my guage is working right? I pulled the wires from the guage and didn't get an OHM reading from the brown wire. When I connected the black wire to the guage and not the brown, the guage dropped to empty. Does this mean there is a bad connection somewhere from the guage to the sending unit? Also, this might be a dumb question, but does tank size matter. The car was originally a six cylinder. Did they make a 15 galloon tank? Might be irrelevant.
 

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I'm confused,
Where did you have the meter leads connected when you didn't get a reading?

There is a black wire AT the gauge?

I may be wrong cause I've never done it but I'm thinking the black wire at the tank is the ground and the brown wire goes to the gauge, so you should disconnect the brown wire at the tank and get an ohmeter reading between the TERMINAL the brown wire came off of and ground.
 

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Discussion Starter · #3 ·
Sorry if I am unclear. Yes there is a two prong connector at the back of the gauge in the dash, one brown, one black. I disconnected that connector so I could get an Ohm reading at the dash from the sending unit. Nothing. The black must be the ground for the guage? The sending unit, in the tank, is fine. It is new. Ohm reading tests fine at the terminal. I pulled the sending unit out of the tank, connected the ground and tested the unit. Arm down, 0 ohms; arm up, 90 ohms. Maybe these two questions will clear things up.

1. Is my guage bad? When I pull the brown wire from the sending unit, the guage reads full. When I fill my tank it reads 1/4 now that I replaced the sending unit. When I unplug the two wire connector from the back of the guage it reads full, when I attach the black wire to the guage, it reads empty. Can I run dumby wire from the guage to the sending unit terminal to test the guage?

2. If my guage is good, how many wire connections are there for the brown wire from the sending unit to the guage? I know there is one in the trunk and it connects the brown wire to a wiring harness similar to the wiring harness in the steering column (flat and thin). Where else is there a break in the connection from the sending unit to the guage. I am going to have to take ohm readings at each connection to find a short if there is one.
 

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Do you have a black wire at the tank sender, that is grounding the sender?

Edit Bad information has been removed.
 

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Discussion Starter · #7 ·
Yes, sender is grounded. Everything is fine at the sender. The black wire at the guage might have a pink tracer. If what you say is correct, my wires are fine. I unplug the wires from the guage and it reads full. I connect the black/pink wire and it reads empty. However, I am a little confused. Should the brown wire read the resistance/ ohm from the sender? Wes Vanns post in tech reference seems to say that also. After all, doesn't the guage read resistance (brown wire)? With the tank full it should read 90 ohms; empty tank, 0 ohms. In your last post you said it should read zero?
 

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Wes Vann is correct, I got it wrong, again.

0 ohms = tank empty, 90 ohms = tank full. Yes you should be able to measure the tank sender resistance from the gauge connection, brown (tan) wire to ground.

"how many wire connections are there for the brown wire from the sending unit to the gauge?"
The brown wire from the gauge to the tank sender has two connections. One is under the dash where the dash harness connects to the body harness, the second is in the trunk where the body harness connects to the rear lamp harness. A good test is to ground the brown wire at the sender, gauge should indicate empty.
 

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Discussion Starter · #9 ·
Okay, I think I can narrow it down. A few more questions. If I ground the brown wire at the sending unit and it reads empty, would I than assume my guage is bad and not the connection from sending unit to guage? See this is what is so confusing. I am assuming that because I am getting a reaction from the sending unit to the guage when I ground or pull the brown wire that my connection is good. There is a signal reaching the guage telling it what to do. However, the guage is acting correctly too by reading empty or full. :mad:

I am guessing that I must have a bad connection because I am not getting an ohm reading from the brown wire at the guage. Unless I am testing it wrong. I use the red lead on the brown and ground the black ohm meter lead to my steering column or something. Do I still need the black wire attached to the guage? It wasn't. However, why would I get a partial reading from my guage when the wires are connected (guage reads 1/4 full when tank is full). Either there is a connection or there isn't right? Okay, I think I just confused myself more. WHY THE HELL IS THIS SIMPLE CRAP SO COMPLICATED!!!! Sending unit, wire, guage, that is all.


By the way, where does the black wire from the guage go? My chilton's book says the temperature switch. I have a few wire connectors that aren't hooked up. I think they are for temperature controls? So does this mean my guage isn't going to work right. Damn, if it isn't one thing its the next. I learned on thing. ELECTRICAL SUCKS!

I have to really thank you guys for taking the time. You have been a great help.
 

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Discussion Starter · #11 ·
Sending unit is fine. I need to check the path from the sending unit to the guage and I need to check the guage. It is one or the other that is bad.
 

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Is it possible the brown wire is pinched or otherwise grounding out on the frame. I think you could test that idea with the ohm meter. Disconect brown wire at both ends. Put one side of meter on end of wire and the other lead to ground.
 

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DJ,
I had the same problem with my Elky. Someone had installed a trailer hitch and tryed to wire brake lights to a trailer lightplug. They hacked into the thin flat floor harness. It was easyer to replace that than try to repair it. These are no reproduced. I found someone in the for sale section at Team Chevelle that had one for sale. All my other wiring is new using aftermaket. I used dielectric greese on all conections to make sure the brass conection do not corrode like on the orginal wiring. Email me if you have anyother questions.

65Camino
Seattle
 

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Have ether the guage or sender been replaced? 64 & 65 look the same but have differnt ohmage. It could cause differnt readings??
 

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I checked my photo library. The correct part number for the 65 SS fuel gauge is 6430197. I have a digital photo if you want me to email it to you. That number should be visible on the gauge face at the bottom.
You must be sure you have the matching gauge and sending unit as 64 ad 65 are not compatible. If your fuel gauge has the above part number, then check to ensue your sending unit is correct of a 65 gauge.
 

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DJ,
Maybe I can help you with your trouble shooting efforts. This may seem long but it may be worth reading and is backed by over 40 years of experience, so bear with me. In about 2 hours you should have the problem isolated and cure defined.

You will only need 2 small rolls of #12 or #14 insulated stranded primary wire, one RED and one BLACK (available at any auto parts store); and a few "clip leads" (you can make your own or pick them up cheap at radio shack). You should also use a digital volt/ohm meter but it's not absolutely necessary. But it will give you the most accurate readings and draw less current from the test point. Also, make sure the gas in your tank is half or over but preferably not full.

Sometimes electrical can be a bear. If you make assumptions rather than prove the circumstance, it will drive you to distraction. If the gauge and sender are indeed the correct units, you only need to verify about 4 things to isolate your problem.

One of the hardest things for people to troubleshoot is a bad ground. Mainly because there's no "absence of voltage or signal" to indicate where or if it exists. So, when I try to trouble shoot something like you are doing, I ALWAYS run a long black piece of number 12 insulated primary wire to the negative side of the battery. Make absolutely certain that this connection is clean and solid. A large alligator clip will do fine. All electrical ground paths lead to there. THAT wire is also what I hook my meter to when I take readings and when grounding other leads like at the back of the guage or the brown wire. I tie every ground of the circuit I'm testing (in this case, the tank sending unit ground and the instrument cluster ground) to that lead also. It only takes a few cheap clip leads from Radio Shack to do this. If things start working correctly when you are doing this, you know the answer, BAD GROUND(s). I never trust that because a ground wire is bolted to the frame or block that it is making a good connection. I've had too many that looked perfect but weren't because of engine paint or frame rust. I always tie my meter to that black lead connected directly to the negative battery post. You'd be surprised how many "wierd problems" I've easily solved this way.

First, forget the sending unit for now, diconnect the brown wire from it and tape up the end from the harness so it's not touching ground. Let's try to verify/isolate one element of the gas gauge circuit at a time instead of dealing with the whole thing and multiple variables.

- Disconnect the brown wire from the back of the gauge. Based on the info from others here, it should peg the full mark since it is now seeing 90+ ohms. If it doesn't, you should stop and find out why not.

- Next, verify there is a good 12 volts supplying the gauge (and the rest of the dash). With the black lead of your meter connected to that "home run" ground lead and read the voltage on the other connection of the gauge, that's the supply side. If 12 volts, proceed. If not, find out why.

- Next ground the Volt meter to the dash frame andd measure the same 12 volts at the same point. If it reads the same as when the meter was grounded to the home run lead, chances are the dash ground is good. If it read differently, you have a bad dash ground. (You can easily clip the home run ground lead to the dash and see if the reading changes. If so, that is a dash ground problem.)

- Now ground (to the home run ground) the side of the gauge that the brown wire goes to. Again, based on the info provided here, the gauge should read empty. If not, you have a bad gauge.

- Now we'll jump to the sending unit because the it's easy to eliminate the wiring in between. Use a piece of RED #12 insulalted primary wire and tie one end to the gauge terminal where the brown wire would normally go. Connect the other end to the the lead from the sending unit that the brown wire should normally connect to. Remember to connect the sending unit ground to the "home run ground lead" even if it's bolted to the frame. If necessary, unbolt it for this test and clip the black wire from the battery to it. Turn the key on and look at the gas gauge. Does it accurately reflect the amount of gas in the tank? If yes, congratulations, you have a bad ground or wiring from the gauge to the sending unit. If not, you have a bad (or wrong) sending unit. If everythnig reads correctly, clean the ring terminal and frame area to bare metal and re-connect the sending unit ground to the frame. Does the gauge still read ok? If not, fix the bad ground connection there, or elsewhere.

Note: at this point you have verified that the gauge works properly and you have eliminated ALL the wiring between the gauge and the sending unit to determine if the sending unit is functioning properly (or repaired it). The only part left in the equation is the wiring between the gauge and the sending unit.

- With the brown wire disconnected from the sending unit, connect the other end back up to the gauge. If the gauge doesn't continue to read FULL, you have a short or partial short to ground in the harnesses between the gauge and the other end of the wire. Stop, find it and fix it. Start by disconnecting the first connector from the tank end and then the next towards the gauge unitl the gauge reads FULL. Fix the short.

- Now ground the other end of the brown wire to the "home run" ground lead. The gauge should read empty. If not, you have a bad or dirty/corroded connection in the brown wire circuit between the gauge and the tank end. At this point you can find and fix it or just bypass the whole circuit with the red wire. Your choice.

Hope this helps.

/herb sr.
 
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