Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

Did you attach the ground wire to the cluster?

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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?

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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..

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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?

Re: Help With New Instrument Cluster, please
 

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

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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?

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

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?

Re: Help With New Instrument Cluster, please
 

I get continuity across it.

Re: Help With New Instrument Cluster, please
 

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.

Re: Help With New Instrument Cluster, please
 

I just tested a factory gauge, and it goes directly to the empty mark when the tan wire post is connected to ground and the other posts are connected to power and ground.

These gauges generally stay where they were last positioned when power is removed. Under normal circumstances, I don't see how the gauge would end up pointing off to the left like yours. It should be somewhere between empty and full, and possibly as far clockwise as 3:00 if the tan wire is disconnected. Makes me think your gauge isn't getting either power or ground.

Re: Help With New Instrument Cluster, please
 

So if want to test this in the truck (cluster plugged in and battery connected) I'd clip my red multimeter to the key on post and clip the black wire to the ground post and turn key to on position to check voltage. Then key off and clip multimeter to ground post and input posts and look for no continuity ? Just want to be sure I'm not going to short anything out this way. Thanks

Re: Help With New Instrument Cluster, please
 

Yes on the voltage test.

For the continuity test, I thought about some more, and it would be better to measure resistance between the tan wire post on the gauge and the ground post. This should be done with the ignition off. You should get somewhere in the ballpark of 45 Ohms (maybe less), depending on the position of your sender. I would also take this same measurement with the brown wire disconnected from the sender. The resistance should be close to 100 ohms.

Re: Help With New Instrument Cluster, please
 

The tan post to ground on back of gauge key off read about 57 Ohms. There's only a tan wire on the sender no brown did you mean that I should disconnect that one at the sender and repeat the same test ?

Re: Help With New Instrument Cluster, please
 

Yes, sorry, tan disconnected at sender

Re: Help With New Instrument Cluster, please
 

OK my turn to mess up. The first reading was with tan wire off sending unit. It read 33 Ohms wire on. that's on my Cen-Tech meter set to 200 in the Ohms section.

Here's what else I know:

Fuel Gauge Circuit Tests
New Instrument cluster, new fuel sending unit. Condition key off: gauge needle 9 o’clock (off top scale). Key on gauge needle moves toward 10 o’clock position.
• Battery: Good
• Fuses continuity: Good
• Wire (tan) continuity from sending unit to fuel gauge fuse block: Good
• Ground at instrument cluster : Good
• Ground from cluster wiring harness to cab: Good
• Ground at sending unit on tank: Good
• Tan wire off post at tank, key on: gauge does not move from 10 o’clock.
• Tan wire on full ground, key on: gauge does not move from 10 o’clock.
• OHMS at new sending unit installed in tank (approx. half tank of fuel): 44

Re: Help With New Instrument Cluster, please
 

The resistance measurements seem a little low, but that doesn't necessarily indicate a problem. It's good that you get two different values with tan wire connected vs. disconnected.

Did you measure the voltage between the power and ground posts on the gauge with the ignition in the run position?

Re: Help With New Instrument Cluster, please
 

My apologies if I'm over cautious as I'm not too well versed in auto electric so to test this in the truck (cluster plugged in and battery connected) I'd clip my red multimeter to the key on post and clip the black wire to the ground post and turn key to on position to check voltage?

Re: Help With New Instrument Cluster, please
 

Yep. Just make sure the clip on the key-on post is touching only the post and nothing else

Re: Help With New Instrument Cluster, please
 

13 volts

Re: Help With New Instrument Cluster, please
 

You've got power to the gauge.

You've got a seemingly good connection to the sender.

The resistance of the sender seems good.

I hate to say it, but I think you have a bad gauge.

Re: Help With New Instrument Cluster, please
 

Also, the 57-Ohm measurement you took of the gauge's internal resistance should be closer to 90 or 100 Ohms.

Re: Help With New Instrument Cluster, please
 

Well those readings plus the grounds being good (as per a test light) and the gauge not reacting to be having the tank input wire (tan) fully grounded and completely disconnected, as well as the the new sending unit reading 44 Ohms (right for half a tank in addition to reading correctly on the old gauge for the old cluster) would seem to point the gauge itself? Am I interpreting this correctly? Are there other tests I should conduct?

Re: Help With New Instrument Cluster, please
 

The definitive test would be to pull your sender out of the tank so you could move the arm and see the needle move (sender flange connected to ground). If the needle doesn't move, then you could reinstall your old cluster and see that the needle moves in the same conditions.. I think you already have enough info to say the gauge is bad though.

Re: Help With New Instrument Cluster, please
 

I'd really like to avoid pulling that sender out but might just do it. What about the amp meter. Is there a test for that I can do while it's installed to see if it the gauge is good? Again my thanks to everyone who contributed to helping me out.