The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Gas Gauge Issue

1966 C-10 Short Step

I just moved my gas tank from behind the seat to the rear of the truck. That went well. I installed the sending unit and grounded the unit to the frame. I ran a new wire from the new sender to the fuse panel and plugged in the wire to the panel. Worked good. I added a few gallons of fuel to make sure the sender worked properly before I reinstalled the bed wood. I moved the truck to the opposite side of the garage and the gauge went to full and stayed there. Tank is approximately half full. I went to the fuse panel and noted that the bottom screw to attach it to the firewall was missing. I inserted a new screw and as I tightened I the gauge worked again. The went to full again and has stayed there - almost like the whole system is grounded.

My question is - is there some form of insulator that goes under the fuse panel - like a spacer or something?

1. The wire from the sender does NOT go to the fuse panel. No no no nono NO! The fuse panel has nothing to do with the sender, just the gauge. If you have hooked up voltage to the sender, you have fried it.

2. How did you ground the "unit"? What did you ground?

3. Hold on with this until you explain ALL the wiring. So we can understand, explain and help.

Basic sender/gauge wiring:
A short wire from sender mounting flange screw, or metal tab, to a clean metal spot on frame.
A long wire from sender center tap to the sender terminal on gauge.
A keyed fused hot wire to the voltage terminal on gauge.
A method to insure gauge ground is grounded to dash structure.
A continuous ground path from gauge ground plate/frame/feature to the battery negative post.
A continuous ground path from the sender ground spot to the battery negative post.

Bartamos - Thanks for your reply. Actually, when I disconnected the wire from the sending unit behind the seat, I thought the same as you stated here. That is, why would there be a connection that goes to the fuse panel? It should go directly to the gauge. However, further research provided that the sensor wire is plugged into the left side of the fuse panel - second spade connector up from the bottom (look at a '66 fuse panel in the internet ) and you can see that spade connector is labeled "fuel gauge". On the backside of the fuse panel - attached to the other end of that spade connector is a brown wire that goes to the fuel gauge. So essentially, the sender wire connects to the fuel gauge though the fuse panel. I don't believe there is any power there - just a connection. And to restate, this all worked after I ran a new wire to the new tank sending unit and made the connection. It was a week after I hooked everything up that the gauge started reading "full". The ground wire from the sending unit is connected to a clean, bare frame connection made on the truck frame near the gas tank. In another post related to backup light issues, another Stovebolt contributor suggested that my '66 may be wired more like a '67. When I was installing the gas tank and wiring the sending unit, the full reading occurred then as well. I finally discovered that if I moved the fuse panel slightly the gauge read the proper level. That is when I discovered that the bottom screw that secures the fuse panel was missing. I replaced the screw - and the gauge worked after I tightened the panel to the firewall. Then, as I said in my post, after moving the truck and driving it a short distance, the gauge went back to reading full. Which is why I wondered if there was some form of insulating spacer behind the fuse panel that kept it from grounding against the firewall. So.. I am still puzzled.

Bartamos - What does, "A method to insure gauge ground is grounded to dash structure" look like. I think this is part of my problem.

Tim-o - I also confirm your arrangement at the fuze panel. I have a post for the sender wire. I assumed it was powered, but never thought about it. I will look at mine again now that you both are teaching me something.

Hambone- tomorrow I intend to test the second wire to the gauge.. I believe it is red. As I stated earlier, the other one is brown and comes out of the back of the fuse panel. Somewhere in reading other posts I saw a reference to an insulator under the fuse panel. The way my brown wire - and the spade connector - on the back of the panel looks - I can see where it might contact the firewall now that I have secured the fuse panel with a second (and lower) screw. Wiring is not my forte.. but I’m trying to figure this all out. Another interesting thing, when my key is off, the gauge reads half full which is about to he amount of fuel in the tank. When I turn the switch on, the gauge goes to full. Tim-o

Well Timo, I kind of get lost on your posts. Just make sure it follow the basic list. The loose screw seems like it causes a spade/wire to become on and off. So clean and tighten all the spade connections involved. As far as the sender, I would forget the spade. Bypass it. Splice so that the sender wire goes directly to the gauge as I said in my first post. Unless you enjoy chasing this around and you want it to act up all the time. I don't care what the internet says. A direct wire is best. No reason to bounce off the fuse panel.

HB: I was being sort of generic. Making sure everyone realizes, as I've tried to explain many times, that grounding "starts" at the component but has a torturous path to the battery post. A path of just touching.... and rivets and screws and bolts and wires and braided straps and spades and solder joints and connectors. Thru rust and paint and corrosion. It's a hard task to achieve after years of aging. It's up to us all to examine it all. Change it to be more solid. Some of the ground ideas from the factory has maintenance in mind. Ease of factory assembly. Building sub assemblies and just plain no good and too many "junctions". I didn't know, and still don't know exactly how a 60 Chevy gauge is grounded. I do know how it is grounded on my 60 GMC and have seen how on TF and AD. I believe they are all basically the same thru 66. Keeping in mind the 66 had "gauge clusters" and "non gauge idiot light cluster", BUT both have a fuel gauge, albeit different looking? Anyway the back of the gauge is the same on all years I've seen. That is: there is a 1/4 diameter round slug that is NOT the ground. It is isolated from everything. The gauge does have a "ground plate". Has a hole for this slug and possibly some other holes and slits. The stud terminals and the slug (meter movement rivet) are isolated from this ground plate. The plate is forced against a metal surface by the terminal nuts. This metal surface is part of the cluster panel (the beginning of the ground path) and you will see by observation how it's ground path is achieved. Thru the cab. Eventually to the battery negative post. The dash structure and path is a little different on each truck era/model. If by testing, a person sees that they have a ground problem with the gas gauge reading, they must observe and inspect and improve the path of the gauge and the sender. In the last month or two I have written "a book" on this issue here on Stovebolt. It's all on the internet in various places. Trying to put it all here in normal terms and reasoning. I need things spelled out for me and tend to write like that.

Bartamos — thank you once again for your time and effort responding to my post. I agree, the most direct path for the signal from the fuel sender to the fuel gauge is a wire that doesn’t pass though the fuse panel. While splicing the wire from the sender and the wire from the fuse block to the gauge together would be a solution, it doesn’t allow me the opportunity to learn what the exact cause might be. Perhaps my 30 years as an auditor analyzing to determine exactly what is wrong — and then fixing the problem identified - is getting in my way of just getting past a problem encountered. To a point, I do enjoy the analysis process because it helps me to learn and apply the lesson learned to future issues encountered. But it is time to move beyond this problem — and this post. Again, thank you for your response.

I have a '63 with stock gas tank, sending unit, and gauge (as far as I know). The gas gauge reads 1/4 all the time. Any help on how to troubleshoot is much appreciated.

Please start your own post. I don't know if you can search because you are moderated. If you can search, there is more info on that issue in here than any other issue.
Glad to help if you can't search.

As bartamos suggested use the search function at the top of this page. Hundreds of threads on gas gauge repairs. Also stop by the Welcome Forum and introduce yourself. Welcome to Stovebolt.🛠