Help With New Instrument Cluster, please

[Zonaman]

Just installed an new instrument cluster in my 69. The gas gauge reads off to the left side not top center. https://photos.app.goo.gl/EpFhFnFRakxQJBMS9. Just prior to installing I replaced my sending unit with a new one and tested it on my old cluster. It showed half a tank which is about what I have. The new one seems to register but not on the top. It's off to the left. Any ideas would be appreciated. Thank you.

[Richard]

Did you attach the ground wire to the cluster?

[Zonaman]

No I didn't. Where is that located? I didn't recall seeing anything when I took off the old one. Thanks

[Zonaman]

Doesn't seem to be a ground wire anywhere that I can see. All the install videos I've looked at don't seem to talk about this. I noted my amp meter ins't working either. All other gauges are good. Any suggestions appreciated.

[Richard]

Check the original cluster. If I recall correctly will be a wire attached to a post with a bare end. The bare end just went into a clip on the column support or surrounding dash metal.

[Thealien]

There is a picture of the ground wire for the dash in the second post of this thread

http://67-72chevytrucks.com/vboard/s...d.php?t=721429

[Zonaman]

Found it. Thank you. The wire is connected as in the thread you referenced.

[Zonaman]

I did install the plastic float as per this post http://67-72chevytrucks.com/vboard/s...d.php?t=666161 when I put in the new sending unit but to reiterate, the old gauge showed half a tank as it should have when I tested it. If the float had come off I'd just be getting "E" all the time would I not?

[BT Classics]

Did the arm on the float move freely?
I once made the mistake of tightening it a little too much. Outside it seemed to work fine. But inside the tank there was just enough resistance so the arm would get 'stuck' in one position. I originally thought it was a gauge problem until I eventually discovered the real culprit and had to take the sending unit back out.

[RustyPile]

Was the old sending unit working properly before you did all this cluster work?? If it's still good, use it to test the gauge. If it isn't good, obtain a known good one or remove the one from your tank. Using a jumper, connect the sending unit "frame" to a good ground.. Connect the brown wire to the post on the sending unit.. Turn on the ignition switch (you can start the engine but it's not necessary).. Slowly swing the float arm through it's range of travel -- 1/4, 1/2, 3/4, and full points.. If the gauge responds but not accurately, you have a problem with the gauge or related circuitry.. If the gauge doesn't respond at all, you probably have a bad gauge, bad connection, or possibly a bad printed circuit..

[Zonaman]

Originally Posted by BT Classics

Did the arm on the float move freely?
I once made the mistake of tightening it a little too much. Outside it seemed to work fine. But inside the tank there was just enough resistance so the arm would get 'stuck' in one position. I originally thought it was a gauge problem until I eventually discovered the real culprit and had to take the sending unit back out.

Yes it did. But I'm tempted to put the original float back just to be sure.

[Zonaman]

Originally Posted by RustyPile

Was the old sending unit working properly before you did all this cluster work?? If it's still good, use it to test the gauge. If it isn't good, obtain a known good one or remove the one from your tank. Using a jumper, connect the sending unit "frame" to a good ground.. Connect the brown wire to the post on the sending unit.. Turn on the ignition switch (you can start the engine but it's not necessary).. Slowly swing the float arm through it's range of travel -- 1/4, 1/2, 3/4, and full points.. If the gauge responds but not accurately, you have a problem with the gauge or related circuitry.. If the gauge doesn't respond at all, you probably have a bad gauge, bad connection, or possibly a bad printed circuit..

I appreciate everyone's help, thank you! The old sending unit was bad but the old gauge was good. I did test out the new sending unit by running it with the old cluster an it was ok. So it looks like I'm going to be pulling out the new sending unit just to be sure about the float and I can jumper that and test it out of the tank. But why would the new gauge register not on the top but left side (see video link above) ? Wouldn't it just register on the top part of the gauge where it's supposed to be either stuck somewhere near "E".or inaccurate but at least within the top of the gauge where the full to empty part is marked? The new gauge is getting a signal but it shows in the wrong place on the gauge face.

[RustyPile]

Originally Posted by Zonaman

....[snip]...But why would the new gauge register not on the top but left side (see video link above) ?........[snip].........

[edit] You have to test the gauge with a KNOWN GOOD sending unit.. Read the last 2 sentences of my previous post...

[Zonaman]

Originally Posted by RustyPile

[edit] You have to test the gauge with a KNOWN GOOD sending unit.. Read the last 2 sentences of my previous post...

The new sending unit registered my fuel level accurately- with the plastic float on the old gauge in the truck. Since it was good on the old cluster I presume it to be good on the new one. That's why I look on the new gauge as the likely culprit. I can pull it and test it just to be sure. I can even put the brass float back on just to be on the safe side

[pjmoreland]

I wonder if your tan wire is shorted to ground, possibly where it connects to the sender? I believe that would cause the gauge to point to the left. With the tan wire disconnected from the sender, the gauge should point to the right (3:00).

There's a lot of helpful information in this post:

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

[Zonaman]

Originally Posted by pjmoreland

I wonder if your tan wire is shorted to ground, possibly where it connects to the sender? I believe that would cause the gauge to point to the left. With the tan wire disconnected from the sender, the gauge should point to the right (3:00).

There's a lot of helpful information in this post:

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

Thank you. I took the tan wire off the sender, key on. It remains as you see it in the video link I posted above- at the top of the scale on the left side of the gauge. It has no effect. Suggestions?

[pjmoreland]

Does your new gauge have a resistor installed on the back of it, like in the link I posted above?

[Zonaman]

Originally Posted by pjmoreland

Does your new gauge have a resistor installed on the back of it, like in the link I posted above?

Here's an image of the back of the fuel gauge as it came from the vendor on the cluster. Is that a resistor? I honestly can't tell.

[pjmoreland]

I agree, it is hard to tell. I am not familiar with reproduction gauges. If there is one, it isn't the same ceramic style that came on these gauges originally. It would be interesting to measure the resistances between the three posts as was done in the troubleshooting guide.

[Zonaman]

I have seen a video from LMC explaining that they don't use resisters on modern reproduction gauges. https://www.lmctruck.com/product-vid...el-gauge-video I bought this one from Brothers so I could ask them. Can this test be done with the cluster installed as it is? It's very tight under there and I'm kinda old & fat - nevertheless, I'd rather not have to pull that cluster out unless I wind up returning it. Also, is there a way for me to test that tan wire? I looks as though it goes from the fuel gauge space on the fuse box, under the carpet and to the sender. Have I got that right?

[pjmoreland]

I agree it is a major pain to work on anything up underneath the dash.

Did your old gauge cluster have temp/oil/battery gauges on it, or was it the simpler warning light style? The reason I ask is because there are differences in the wiring harness for the two types of gauge clusters. One of the differences is the connector pin that provides power for the fuel gauge.

[Zonaman]

Originally Posted by pjmoreland

I agree it is a major pain to work on anything up underneath the dash.

Did your old gauge cluster have temp/oil/battery gauges on it, or was it the simpler warning light style? The reason I ask is because there are differences in the wiring harness for the two types of gauge clusters. One of the differences is the connector pin that provides power for the fuel gauge.

Same as the new except the new one has a clock and tach- both of which are functioning perfectly and are wired directly from the fuse box although both get their ground from the cluster. Everything is working except the the fuel guage and the amp meter. Temp gauge is working, Speed and oil pressure don't really count since they're not electrical. Lights all good.

[pjmoreland]

Running through the tests outlined in that LMC video should help you pinpoint the problem. If you've got test leads with alligator clips, then you should be able to fasten them to the gaige posts and then do all the tests while sitting on the seat. Unplug the big black connector from the back of the cluster to isolate it from the truck during the tests.

Is your Cluster Feed fuse still good?

[Zonaman]

I get continuity across it.

[pjmoreland]

If it were me, the next thing I would do would be to verify the presence of 12 volts across the power and ground posts on the gauge with the key in the run position. I would also make sure there isn't continuity between the input post (connects to tan wire) and ground.