fuel gauge fixed - studs not touching metal case

[hmaynord]

shout out to PowerMan for this fix:

It will peg because one of the pegs on the gauge is touching the metal gauge cluster. Dealt with that before. You loosen the nuts holding the gauge and make sure it's not touching the metal. Hopefully that will work out.

Thank you Powerman for posting this... I was pulling my hair out on this exact problem until I loosened the nut and moved the fuel gauge over about 1/4 inch and..... I have a working fuel gauge! Oh and the temp gauge is working again!!! I am in business... Thanks for this post, I know it is two years later.. but thanks!

To make a long story short, I changed the sending unit, the gauge, the wire between them, and added a ground wire to the tank. Still had intermittent problem where gauge would peg at max. Did this fix about a month ago, and no more problems.

took me a while of searching to find this fix, so figured I would bump it up.

thanks PowerMan.

[PIRATEUSAF]

I have fried three gauges.
Hook up the 12 volts to the appropriate terminal on the gas gauge and bam… starts smoking !!
I have to wonder if I have it shorted out somewhere.

[PwrWgnDrvr]

I have fried three gauges.
Hook up the 12 volts to the appropriate terminal on the gas gauge and bam… starts smoking !!
I have to wonder if I have it shorted out somewhere.

Yes, you have a short somewhere.
That's called the "smoke test"....used for finding shorts.

[PIRATEUSAF]

I hooked a test light to the wire coming from the fuel tank sending unit. The test light came on so I know the sending unit is grounded. I have to believe that the gauge itself must be grounding out on the metal gauge housing unit that mounts inside the dash.

[martincom]

Can you post some photos of the back side of instrument cluster? All my service manuals are packed for the move, so I'm not exactly sure what you have.

[712edf]

Sending units have a variable ground, based on the amount of gas in the tank. Empty tank provides very little ground so the needle doesn't move much if at all. Full tank provides more ground continuity to the circuit & moves the needle more. But even with a full tank of gas a properly working sender still has enough resistance to keep from pegging the needle & burning up the gauge.
The sender is like a rheostat (dimmer) that the float controls.
These should be checked with an Ohmmeter not a test light.

Bucky

[martincom]

Do you have the ground wire connected to the instrument cluster frame? Is it a solid connection? For the voltage limiter to function correctly, the instrument cluster needs to grounded. If there is no ground or a poor ground connection, it will not function and will likely pass full battery voltage to the instruments. This could be what is causing them to "burn up".

On my '71, the ground wire is a white #12, that connects under the mounting screw for the filter condenser (capacitor). The other end connects under the mounting screw for the headlight foot dimmer switch. That is not the best place either, as it is even often rusty/corroded from wet floor mats, windows left rolled down, etc.

I'm just guessing, as the information you have conveyed is limited.

[Wildergarten]

On my '71, the ground wire is a white #12, that connects under the mounting screw for the filter condenser (capacitor). The other end connects under the mounting screw for the headlight foot dimmer switch. That is not the best place either, as it is even often rusty/corroded from wet floor mats, windows left rolled down, etc.

I'm thinking connecting to a an all-thread stud throughbolted to the firewall where the ground strap is mounted in the engine compartment between the firewall and the block would make a good body ground. Even better with star washers against the sheet steel inside and under the nuts clamping the lugs (total of three).

[martincom]

I'm thinking connecting to a an all-thread stud throughbolted to the firewall where the ground strap is mounted in the engine compartment between the firewall and the block would make a good body ground. Even better with star washers against the sheet steel inside and under the nuts clamping the lugs (total of three).

Agreed. I adopted a quote from a mentor: "A good electrical connection begins with a good mechanical connection."

I can't tell you how many times I've seen the sheet metal screw block to firewall ground connection stripped out at the firewall. I insert a 1/4 x 1" bolt through the firewall, from the interior, and utilizing a piercing star washer beneath a flat washer on the engine side, making a stud type point for ground connections.

Up until 1970, this was the body ground connection on Mopar passenger cars. After that, they changed and added a tail to the negative battery cable, which was the body connection, typically at the core support. Whenever I find the need to replace a negative battery cable, I always utilize this type with a molded on clamp and a tail long enough, where it doesn't have to be spliced. Typically, I use battery cables from a Hemi application, as they are #4 rather than #6 gauge.

[Wildergarten]

Typically, I use battery cables from a Hemi application, as they are #4 rather than #6 gauge.

Totally with you there, especially about the star washers. I use those on all bolted electrical connections.

I'm going to be running either a #4 or #2 all the way to the back of the truck to run the compressor and accessories with a stopoff along the way to run an inverter. I'm thinking the The latter will be kept in the cab (more room and better cooling than in an underbody box, although I do have two fans in series going into one of them to cool the compressor so I could put a switch in parallel with the compressor for those in there). In fact, with the dual battery system with an isolator, I'm contemplating putting jacks inside one of the underbody boxes for welding cables! My Harbor Freight MIG died recently and I cannibalized it for the bulkhead connectors.

I've never stick welded from a battery and I'm not anticipating doing a lot of welding. It's just an emergency capability that could come in very handy working on the land far from a power source I'm thinking would be a potent resource for the neighborhood where we live. The alternative is to get a 220V inverter to run the wire-feed machine but I've read that welders are hard on both generators and inverters.

[martincom]

Motorola supplied a star washer, for the ground ring, on their high high power radios. They're about the size of a 1/4" USS flat washer in diameter. I'd take a photo of one, but the service truck is getting the rear bumper/trailer hitch rebuilt---rusted away in just 14 years. Anyway, I've got more than I'll ever utilize. PM me your address again and I'll mail you some.

I utilized #2 welding cable to feed power to the rear bench area of our service trucks. I fabricated some bus bars from aluminum stock and lug terminals. See the photo below. We ran 1000 watt inverters. At a full load, they'd draw near 70 amps. We had two-way radio equipment, our service bench had 12 volt banana plug receptacles, 12 volt fluorescent lamps, 12 volt soldering irons, etc. We never had a need for mobile welding equipment.

We run a starting battery and two auxiliary batteries in the service trucks. The first two I built I utilized battery isolators. They take up a fair amount of room, so it was difficult to find a good mounting location. I had one fail, also. The step van pictured has a 2008 Ford E450 stripped chassis under it. There was provisions in the wiring harness for a an auxiliary battery relay. When the ignition is off, the relay de-energized and isolates the auxiliary battery(s) and the auxiliary battery terminal of the 7-way RV trailer receptacle from the starting battery. So on this truck, I just went with the relay rather than a battery isolator.

Ford mounted the diesel equipped E450 battery along the frame rail as well as the auxiliary battery. A diesel wasn't an option with a stripped chassis, but I did order the battery boxes and mounting hardware. I sprayed the boxes with bedliner. They have held up very well for a MN truck.

[PwrWgnDrvr]

..... We ran 1000 watt inverters. At a full load, they'd draw near 70 amps....

Nice setup!
How does it draw only 70 amps at full load when P=EI? Only good for 80% of rated output?

[martincom]

I said near 70 amps. Of course this will change with supply voltage. Maybe 12 volts, to start, without the truck running. Maybe 13.5 volts with it running at idle, near 15 volts at 900 RPM or greater.

[Wildergarten]

Motorola supplied a star washer, for the ground ring, on their high high power radios.

I thought I'd elaborate a bit on star washers versus split washers for electrical connections, as a good mechanical connection is not the whole story. The star washer washer makes many penetrations between mating surfaces versus one of them with the split washer. The star washer thus distributes the flow of current through more contact points, which reduces the resistance heat generated in the micro-welds at the points of contact forming the pathway for conductive transfer (primarily tunnelling electrons) and distributes that heat into more of the surroundings. It spreads the bulk flow of electrons into more metal as well, which reduces the heat generated within the wire conductor until that current is distributed within it. It also does a better job of cutting through paint, oxides, and other barriers to electrical conductivity on mating surfaces.

The best resource I've read on this topic is the Ney Contact Manual.
https://www.amazon.com/Ney-contact-manu ... B0006CB8BC
It is an outstanding reference for the design of switchgear.

The big downside to star washers is that they don't support axial compression forces as well as split washers, especially in terms of damage to sheet metal. Both are supposed to be replaced with every use, but I think that more true of the star washer than the split.