gauge cluster help!!

[1972BlueC20]

Hey guys!

So I've been having trouble with getting my fuel gauge to work, I replaced the sending unit and the fuel gauge still doesn't work. So after chatting on here and getting opinions, I've decided to replace the fuel gauge and the wire that runs from the sending unit to the fuse panel. I've ordered a new reproduction fuel gauge and sending unit wire, and while I'm at it, I've also ordered a new dash bezel to freshen it up. The old one is a bit faded.

I've pulled the cluster out just now and taken some photos of everything inside. Before I tear into it and replace the gauge and bezel, I wanted you experts to have a look inside the dash at the wiring.

Some of you mentioned that my issue with the fuel gauge might be caused by a wiring issue or bad ground.

There is one wire that is running from a screw just above the parking brake on the metal part of the dash and was attached to a screw on the backside of the instrument panel. I'm assuming this is the ground?? It's the red wire on the far left in the photo. Is this factory?? Is this sufficient for a ground??

Also how does the rest of the wiring look? Does anyone see anything wrong that could be causing the fuel gauge not to work?

There was also one other wire that was attached to a bulb housing, I think it was the driver side turn signal light bulb connector. Is this correct and factory as well??

Here are the pics!

Let me know if everything looks good before I tear into it tomorrow after work.

[Nitis]

That's actually the fiber optic to illuminate your gear selector

[1972BlueC20]

Thanks that makes sense, so it just channels light from the bulb to the gear selector?

[Nitis]

That's basically what I figured out

[michael bustamante]

From whay ive seen the ground wire is a black wire that has a pinch style clip on it. Basicalll you push the pinch clip onto the lower lip of the dash

[1972BlueC20]

Anyone have anything else to add? Does the wiring look ok?

I'm going to reinstall the gauge cluster today after work, so I want to make sure I don't need to do any wiring / repairs before I button it all back up.

[68gmsee]

Originally Posted by 1972BlueC20

Anyone have anything else to add? Does the wiring look ok?

I'm going to reinstall the gauge cluster today after work, so I want to make sure I don't need to do any wiring / repairs before I button it all back up.

As Michael B mentioned. On my 68 there's a small black wire that goes from the gauge cluster to metal part of dash panel and attaches with a push on clip.

The biggest ground problem most of us have encountered on these trucks is the main ground to battery negative. When fairly new the engine to cab strap, the cab to frame bolts, bed to frame bolts and even the radiator support bolts all completed the loop to battery ground. With age, rust and grime they no longer do the job. I installed 5 ground strap on my truck to create new ground loop years ago.

[GuyO]

It looks like your cluster and wiring are in excellent shape. Also, it looks like your red wire is a ground from the cluster to the parking brake area. I would have used black and like 68 & Michael said, clipped it to the dash metal. Maybe you could rub the contacts with 200 grit before you plug everything in and I like to step up to LEDs (4) for the cluster lights! I had a problem once with a gauge and cleaned the clip on the cluster plug and the gauge started working! Good Luck.

[franken]

Deleted.

[TBONE1964]

Originally Posted by 1972BlueC20

Thanks that makes sense, so it just channels light from the bulb to the gear selector?

Yes, that is exactly what it does. If that bulb ever burns out, not only will there be no light in the cluster in that spot, your gear selector light will not illuminate. You have to be careful not to kink the fiber optic or it will restrict the flow of light.

[TBONE1964]

Originally Posted by 1972BlueC20

Anyone have anything else to add? Does the wiring look ok?

I'm going to reinstall the gauge cluster today after work, so I want to make sure I don't need to do any wiring / repairs before I button it all back up.

I attached a diagram of the cluster connector for you. You can check

and make sure everything is in the correct location on the connector with it.

If you have a DVOM or a 12V test light you can check terminal #6 and make sure it is a ground as it should be. Hook the other end to a 12V positive and touch on the #6 terminal and iut should light the test light or show voltage on a meter.

The number 7 terminal is the pink 20 gauge wire from the ignition switch. You can also check it for voltage with the test light or DVOM. It should only be hot when the key is in the run position.

The number 4 is your tan wire from the sender. make sure you show it has good connections on both ends.

Can you explain what exactly is the problem with the fuel gauge? I am not sure if you mentioned it.

Please ask any questions you have.

Take care,
Tom

[michael bustamante]

Oh and if you het a chance replace that ground strap from cab to frame

[1972BlueC20]

Here is what was happening with the gauge, this is taken from a previous post I made :

"Replaced sending unit, still doesn't work heres what's happening :

This is what happens, when I fill up the needle stays where it was prior to filling up until I drive like 3 miles down the road. Sometimes it even takes till the next day. It then shoots just barely past full. From there it seems to work fairly accurately. It goes down a little everyday as I drive and put more miles on her. Since I'm not sure of the gauge, I always keep track of the miles driven so I don't run out of gas and get stranded on the side of the road. Once I have only about 1-2 estimated gallons left it only goes as far towards empty as a 1/4 of a tank. It may go further down towards empty if I drove somemore, but I'm too scared to run out of gas

When I remove the wire from the sending unit or remove it at the fuse panel there is no change on the fuel gauge.

Anyone have any idea what needs to be fixed or replaced??"

[1972BlueC20]

As for the ground strap on the cab, where is it located so I can check the condition it's in?

[snipescastle2]

If I recall correctly, my 71' the ground straps were just below the opening where the steering column exit's the cab, and on the oposite side below the heater/evaporator area. these were flimsy copper braided straps anyway, might want to step up to a larger size ground cable just to make sure you have a good ground.
Ben

[TBONE1964]

Originally Posted by 1972BlueC20

Here is what was happening with the gauge, this is taken from a previous post I made :

"Replaced sending unit, still doesn't work heres what's happening :

This is what happens, when I fill up the needle stays where it was prior to filling up until I drive like 3 miles down the road. Sometimes it even takes till the next day. It then shoots just barely past full. From there it seems to work fairly accurately. It goes down a little everyday as I drive and put more miles on her. Since I'm not sure of the gauge, I always keep track of the miles driven so I don't run out of gas and get stranded on the side of the road. Once I have only about 1-2 estimated gallons left it only goes as far towards empty as a 1/4 of a tank. It may go further down towards empty if I drove somemore, but I'm too scared to run out of gas

When I remove the wire from the sending unit or remove it at the fuse panel there is no change on the fuel gauge.

Anyone have any idea what needs to be fixed or replaced??"

OK, now I remember from your last post. Have you tried the new gauge yet? As I mentioned before, your problem does not sound to me like a wiring or ground issue at all. It sounds like your gauge is just slow to react. I could be wrong and it has not been the first time.

I would try a new fuel gauge at this point and see what happens.

[No8Easy2]

I agree with Tom on this sounds more like a gauge problem but
why not just check the gauge itself, is the cluster still out of the truck?
if so..

1st you need some resistors so run to radio shack and get 47 ohm and 100 ohm resistors, there cheap and a pack of alligator jumpers

2nd you need to run 12 volts to "B"

3rd make sure to ground the cluster "C" to the truck

then jump the 47 ohm resister between "A" and "C" the needle should go to around half scale,

then used a 100 ohm between "A" and "C" should go to full if the gauge is good

good luck
Chris

[1972BlueC20]

Update :

So I got a new dash bezel (because it was old and faded), new fuel gauge and new wire that runs from the sending unit to the fuse box. I changed the cluster onto the new bezel and changed out the fuel gauge with a new reproduction gauge from LMC and new wire from sending unit. I made a longer wire for the ground wire, it was originally going from just above the parking brake on a screw to a bolt on the inside of the cluster near the speedometer. The wire was very short anyways and was hard to work with because it didn't have enough slack when trying to get the cluster in and out. I took the new longer wire and ran it from the bolt near the parking brake to a small bolt right next to the actual fuel gauge on the back housing.

I buttoned everything back up and viola! The fuel gauge is now working!!!!

We shall see if everything stays working, but so far so good.

Thanks for everyone's help!!