#121  
Old 04-02-2014, 10:05 AM
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Originally Posted by Old Goat 67 View Post
That voltage reading is a good way to troubleshoot, but my question is whether that is open circuit or not?

If circuit is open at sender, you should read 12V then. If connected to sender it indicates that sender is flowing current through it.
Hmm. Not sure I'm totally following you here. My understanding is that while the gauge receives 12v in, the lead out of the dash to the sending unit is generally lower than 12v. Regardless, I tested with that lead wire unplugged from the sending unit at the tank and with the key ON. Does that answer your question?

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  #122  
Old 04-02-2014, 10:10 AM
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You bring up a good point Pepi.

There should be some lesser voltage, because the resistor in the gauge should allow some flow thru the two coils left in the circuit while the sender is disconnected. I would have to go out and disconnect to see how low it might go. I've done that reading before but cannot remember what is read exactly, I was just looking for an open circuit voltage presence at that point back at the sender.
I'd go do it now, but I just don't have the time today.

Adam, the grounding test at the ribbon connector under the carpet would still be a good test for proving or disproving the gauge and dash wiring to be good.

Charles


Last edited by Old Goat 67; 04-02-2014 at 10:16 AM.
  #123  
Old 04-02-2014, 10:28 AM
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...

Adam, the grounding test at the ribbon connector under the carpet would still be a good test for proving or disproving the gauge and dash wiring to be good.

Charles
When I grounded at the ribbon behind the rear seat, nothing happened. That's what's really odd. And I had a very good ground there.

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  #124  
Old 04-02-2014, 10:54 AM
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When I grounded at the ribbon behind the rear seat, nothing happened. That's what's really odd. And I had a very good ground there.
Then you have to go up further to the next connection and try it. If there is one between where you did it and the gauge, other wise yes, ground out on the back side of the gauge. You said the back side of the gauge was an L shaped plug, can you unplug it and stick a wire in from the back and then plug it back in and ground the wire? I don't know how much room you have up there to work. Otherwise not plug the plug on completely and try to touch the metal tang with a pick or flat screwdriver with a wire attached to it and ground out, probably will need someone else to watch the gauge when you it that way since you'll be on your back trying to work behind the dash.

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  #125  
Old 04-02-2014, 11:10 AM
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Adam,

There should be a connector to the ribbon right under the carpet by the kick panel. Try Pepi's test there. Could be an open ribbon cable......

If still no good, that only leaves the Tan wire to the gauge and then the gauge itself.

Charles

  #126  
Old 04-02-2014, 11:12 AM
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Adam, I printed out the wiring diagram you posted and don't see another connector on it, not saying for sure there is not another one, but to me it sounds like a bad wire from gauge to your connector you are checking where it drops to .8v.

You could try probing the wire between the gauge and where you disconnected the flat ribbon at different areas. Just take a pin to pierce the wire insulation and then touch your multi-meter to the pin and ground and check voltage. If you get your 2.8v try grounding it there and see what the gauge does.

That troubleshooting will do several things. If you get 2.8v then you know the wire is broken further back closer to the tank, and if the gauge moves, that is the problem a broken wire. If you don't get your 2.8v repeat the same procedure closer to the gauge. Keep doing it until you get the voltage. I don't know how much voltage gets lost through the gauge, but this helps find the voltage lose in the wire due to a bad wire. Just repeat the process going to the tank to narrow down where the break could be.

The reason I say use a pin is so you don't put big holes in the wire insulation. You could always put a little rubber cement or something where you probed the wire so you don't have an opening for corrosion to start on the wire.

Charles, I was typing as you posted, I thought there should be another connection somewhere, but didn't know for sure.

Adam if it works at the kick panel, ohm out the flat ribbon wire and I sure you find a break or very high resistance.

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Old 04-02-2014, 11:22 AM
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Just to back up a few steps, when I was working behind the seat, I unplugged the ribbon from the rest of the wires. I was able to get the same 2.8v at the ribbon. So that made me feel good since it will be easy to run a wire from there to the sending unit.
HOWEVER, when I grounded that wire, the gauge still read FULL. That's what got Clay and I to think i need to check the gauge itself. Maybe I have two problems, a bad wire and a bad gauge.

So I'm trying to work on the gauge for now. I need to get that to read E before I change any wires on the car downstream of the dash.

I'm going to try and flip the "L" connector over so that I get power to the gauge, but can access the sending until tab with my meter (Clay's idea).

Clay also suggested I take some OHM readings on the gauge alone, no wires plugged in to it. I should be able to do that.

I'll report back.

Hey, while I'm scraping my hands behind the dash, is that where I grab the bulb to replace it? During all my messing around, i blew the dash bulbs. I have to check all the fuses first to make sure they're getting good connections. So many little problems, so little time. But, I'M SO HAPPY TO BE PLAYING with my new toy!

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  #128  
Old 04-02-2014, 11:23 AM
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Pepi,
Drawing is weird there. There are two rectangular connector blocks up there on top left.
One has only 4 wires, other one has 7???
Tan lead only goes through one? Could that mean that it represents the ribbon cable itself with connectors on either end?

The one with four would be near the tail panel for the light wiring?

Charles

Link posted again for clarity.
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  #129  
Old 04-02-2014, 11:38 AM
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Originally Posted by Old Goat 67 View Post
Pepi,
Drawing is weird there. There are two rectangular connector blocks up there on top left.
One has only 4 wires, other one has 7???
Tan lead only goes through one? Could that mean that it represents the ribbon cable itself with connectors on either end?

The one with four would be near the tail panel for the light wiring?

Charles

Link posted again for clarity.
Yes, I think you are right. When I look at that connector, (when I printed it out, it cut off half way through the top bulb) right above it shows the door switch. Obviously that wouldn't be back by the rear connector . So your though of it representing the ribbon cable would be something I would put money on.

Adam, I forgot you were getting 2.8V at that one point and still couldn't get gauge to read correctly. Turning the connector around on the gauge is a good idea.

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  #130  
Old 04-02-2014, 11:47 AM
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Quote:
Originally Posted by Old Goat 67 View Post
Pepi,
Drawing is weird there. There are two rectangular connector blocks up there on top left.
One has only 4 wires, other one has 7???
Tan lead only goes through one? Could that mean that it represents the ribbon cable itself with connectors on either end?

The one with four would be near the tail panel for the light wiring?

Charles
Charles, I think you are correct. I can at least confirm that what we're referring to as the ribbon here is for sure the rear end of the ribbon based on how the sending unit wire comes out of that ribbon behind the rear seatback, through the floor and directly to the sending unit.

Whether that rectangle represents the entire length of the ribbon or not? It makes sense to me since there's no other end of it shown.

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  #131  
Old 04-02-2014, 07:00 PM
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UPDATE:

Good news, bad news. The good: I know what the problem is. The bad: it's my fuel gauge.

I did the following: plugged the harness into the gauge by turning it 180* (thank you Clay). This allowed me to get power to the gauge, while exposing the terminal for testing.

Clay took an unmounted fuel gauge today and took voltage and ohm readings for me. He got about the same volts coming out as was going in. For ohms, there was about 130ohm on one side (terminal to ground), and about 85ohm on the other for a difference of 45 ohm. Then he took a reading across the gauge and got 45ohm.

On my gauge, I wasn't able to get any constant, decent volts coming out to the sending unitl. Then I grounded that line and the gauge stayed on FULL. Finally, I moved on to the ohms. I got 130ohm on B+ side to ground, and 0ohm on the other side. When I measured across the gauge, I got 0.

So, sounds to me like my gauge is shot. All in favor of that diagnosis, say aye____...

So, my only question now is, who's got a `64 fuel gauge they're not using?

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  #132  
Old 04-02-2014, 07:14 PM
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Sounds like the gauge to me. Good to hear you might have it figured out. Once you get a gauge and verify let us know for sure.

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  #133  
Old 04-02-2014, 07:26 PM
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Aye.

  #134  
Old 04-02-2014, 11:32 PM
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I have an extra '64 GTO Fuel gauge here.

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  #135  
Old 04-02-2014, 11:58 PM
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PM sent

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  #136  
Old 04-06-2014, 11:21 PM
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Well, I installed a new fuel gauge today from Pete. It's a correct, 1964 gauge unit, so it should be the correct match for my sending unit. So far, it appears to be working. It's a big hard to tell since I have a full tank of gas currently, but I do think it's sitting at F but not pinned above F, which makes sense since I used about 1-2 gallons coming home from the gas station.

Hopefully, it's functional now. I'll report back after i drive it on wednesday.

Thanks everyone.

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  #137  
Old 04-08-2014, 09:21 PM
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ok, so I put another 20 miles on and the gauge appears to be working! wahoo! I've done 38 miles since filling up, and at 8MPG, I should be showing around 7/8 of a tank. Well, the needle is NOT pegged on F, and it appears to float up and down around the 7/8 range as i go up and down hills (I forgot just how inaccurate the old systems were LOL). so I think it's fixed.




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  #138  
Old 04-08-2014, 09:27 PM
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I say you've got her then. Glad to hear. Now, did you get the rear harness yet?

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  #139  
Old 04-08-2014, 09:34 PM
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Yes, I received the harness. I also bought the correct single element bulbs for the center sockets. I put the bulbs in and everything is working well so I will wait on the harness for now. My turn signals are still irregular in pattern, but they all work so I'm moving on to other projects first.

Let's see: new tach, check. relocated aftermarket gauges, check, removed aftermarket radio, check. Next up: heater core install, glove box and then clay the entire car!

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  #140  
Old 04-09-2014, 09:21 AM
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